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Stacking the deck


XFX's Radeon HD 7950 Black Edition

Even before we received a reference version of the Radeon HD 7950 from AMD, XFX's custom Black Edition of the card touched down in Damage Labs. This card is based on the same circuit board design as the reference cards—board makers haven't yet had a chance to build enhanced or cost-reduced versions of the PCB—but otherwise, it has been transformed with XFX's own cooler and a swanky custom expansion slot cover with a red DVI port.



With dual fans and that lightweight aluminum shroud, the XFX cooler looks like an obvious upgrade from the stock unit, though we'll have to test it to be sure. Believe it or not, the more important changes to XFX's 7950 Black Edition aren't visible to the naked eye.

You see, for several years now, AMD has set the default clock speeds for its GPUs relatively high, leaving little wiggle room for individual board makers to create hot-clocked Radeon cards. Meanwhile, Nvidia has left ample headroom in its lineup, and board makers have taken advantage by shipping a much broader variety of GeForce cards, some with pretty drastically increased default clocks. Although it wreaked havoc at times on our carefully laid plans for testing equivalent products, Nvidia's looser business model created some nice options, especially for smart customers.

With the Radeon HD 7900 series, AMD has decided two can play that game. Tahiti seems to have quite a bit of headroom in it, and board makers are capitalizing on that fact. The default GPU core clock for XFX's Radeon HD 7950 Black Edition is 900MHz, a full hundred megahertz beyond the 7950's stock speed—and only 25MHz shy of the 7970's. What's more, the 7950 Black Edition's memory runs at 5500 MT/s, exactly matching the stock 7970 both in transfer rate and total bandwidth. XFX says the 7950 Black Edition will fetch $499 at Newegg, so the performance gains won't come for free, but this card should come extremely close to matching the 7970's real-world performance for that price.


XFX's Radeon HD 7970 Black Edition

That's not to say the 7970 is entirely threatened by hot-clocked 7950s. AMD's apparent policy change extends to the Radeon HD 7970, too, courtesy of the Tahiti chip's ample clock speed headroom. Pictured above is XFX's 7970 Black Edition, with the same dual-fan-and-aluminum cooler. This card's default GPU core speed is a nice, round 1GHz; its memory clock runs a bit faster than stock, too, at 5700 MT/s. That's enough to give the 7970 Black Edition a clear edge on the 7950 Black Edition, restoring balance to the Force.

The arrival of these hot-clocked Radeons in Damage Labs presented us with something of a dilemma. With fairly wide gaps between the different variants, we'd prefer to test both the stock-clocked and hopped-up versions of each, but time constraints made that impractical—as did our fancy new GPU testing methods, which we believe are the best in the industry, but which require a lot more manual intervention than a scripted test that spits out an FPS average. What to do?

Well, for some time now, our means of dealing with hot-clocked GeForces has been to ensure that we're testing actual, shipping products and then factor both the higher performance and any price premium into the mix. Now that similarly hopped-up Radeons have finally arrived, gosh darn it, we're going to keep that approach and go for broke, with hopped-up cards nearly across the board. After all, we've already tested the stock 7970 in our initial review. Also, we wanted to include a 3GB version of the GeForce GTX 580 in the mix, and the only one we had available was a hot-clocked board from Zotac. Yes, this review will be a little bit like a home-run derby involving Barry Bonds and Mark McGwire at the height of their, er, chemically enhanced powers. Or, you know, like the old SNL skit about the all-drug Olympics:

But at least most of the key participants will be on the juice.

Of course, even without all of these varied clock speeds, the big two GPU makers have a crazy number of fine gradations in their product lineups—especially Nvidia, at present. Tracking 'em all can be daunting, as the table below illustrates, and it's limited to the cards we tested along with the stock reference clocks from the GPU makers.

GPU core
clock
(MHz)
Peak pixel
fill rate
(Gpixels/s)
Peak bilinear
filtering
int8/FP16
(Gtexels/s)
Peak shader
arithmetic
(TFLOPS)
Memory
transfer
speed
(MT/s)
Memory
bandwidth
(GB/s)
GeForce GTX 560 Ti 882 26 53/53 1.3 4008 128
Asus GTX 560 Ti 900 29 58/58 1.4 4200 134
GeForce GTX 560 Ti 448 732 29 41/41 1.3 3800 152
Zotac GTX 560 Ti 448 765 31 43/43 1.4 3800 152
GeForce GTX 570 732 29 44/44 1.4 3800 152
GeForce GTX 580 772 37 49/49 1.6 4000 192
Zotac GTX 580 AMP²! 815 39 52/52 1.7 4104 197
Radeon HD 6950 800 26 70/35 2.3 5000 160
Radeon HD 6970 880 28 84/42 2.7 5500 176
Radeon HD 7950 800 26 90/45 2.9 5000 240
XFX HD 7950 Black 900 29 101/50 3.2 5500 264
Radeon HD 7970 925 30 118/59 3.8 5500 264
XFX HD 7970 Black 1000 32 128/64 4.1 5700 274

Just think. Half of the folks who found this article via Google glanced at that table, their eyes glazed over, and they left to go find a video review on YouTube where some dude raves about frame rates for three minutes. Those of you still left will understand how minor the differences between the different models of cards can be.

We'll admit the new Radeons have some of the biggest deltas we've seen between stock and hot-clocked versions of the same model, which is why we've taken a closer look at all of the different 7900-series variants in the later portions of this review, including some performance testing and the power and acoustic tests. In the earlier pages of this review, please note, the Radeon HD 7950 and 7970 and all of the GeForce models will be represented by hot-clocked cards.

One other dynamic we should point out is the very tight grouping of several Nvidia cards, including the GeForce GTX 560 Ti 448 and the GTX 570. As we said in our review, the GTX 560 Ti 448 amounts to a temporary price cut on the GTX 570. At 765MHz, the Zotac GTX 560 Ti 448 card performs almost identically to the stock GTX 570 but costs less, so it's easily the better buy. Given those facts, we've chosen to exclude the GTX 570 from this contest.

Another look at geometry throughput
Since we've already covered Tahiti and the GCN architecture in some depth in our Radeon HD 7970 review, those who are unfamiliar with this chip owe it to themselves to read that article before finishing this one. Before we move on, though, let's pause for an architecture-related note. One thing we saw in that review was relatively poor performance from 7970 in TessMark, a problem we attributed to driver issues, since Tahiti is purportedly much improved for tessellation. Now, AMD claims to have resolved those driver problems. Here's how TessMark looks with the new drivers.

Wow. In our original review, the 7970 scored so well in our Direct3D tessellation test with Unigine Heaven that we attributed its victory, potentially, to other factors like pixel shader throughput coming into play. Now, we have to reevaluate that sentiment. Looks like the 7970 is legitimately as fast as, or faster than, the GeForce GTX 580 with moderate to high levels of tessellation. As one might expect, the 7950 isn't far behind the 7970 in TessMark, since the clock speeds of the two XFX cards are only 100MHz apart.

Now, on to the games...