Up for a couple of value scatter plots before we call it a day? As is our custom, we've laid our performance results (based on the overall average performance from our game tests) along the Y axis and the cards' pricing (obtained from Newegg, when possible, or from the manufacturer's suggested e-tail price) along the X axis. The most desirable offerings will be the ones closest to the top left of the plot. The least desirable ones will be at the bottom right.
We can also compile a value scatter plot out of our 99th percentile frame time data. For consistency's sake, we've converted the frame times to frame rates, so desirable offerings are still at the top left.
No doubt about it, XFX demands a sizable premium for somewhat modest performance increases—perhaps not in the case of the 7850 Black, which underperformed due to a potential bug that's probably temporary, but definitely for the 7870 Black. $40 is a lot to pay for such a small jump over stock performance, and the fact that the card doesn't overclock as well as the reference model makes it even harder to recommend.
The XFX 7870 does have a couple of redeeming features. Its cooler, though ill-equipped for high overclocks, is much quieter than AMD's design at stock speeds. That might sweeten the deal for folks who care about noise levels—although we should point out that other cards with large, dual- or triple-fan coolers can be had for as little as $360. We haven't tested those, however. Also, there's the lifetime warranty to consider. XFX is one of very few vendors to offer that particular perk.
Nevertheless, considering our past experience with XFX's Black Editions, I must confess to being a tad disappointed by these two cards. Even if you don't mind paying a premium, there are deal breakers in both cases: the 7870 cooler's inadequacy when it comes to overclocking, and the 7850's weird performance issues, which negate the benefits of its higher clock speeds in Battlefield 3, Crysis 2, and perhaps other titles.
If XFX can resolve the latter, the 7850 Black could be a tantalizing choice. We've seen in Arkham City and Skyrim that it comes awfully close to the stock Radeon HD 7870—and we've also seen that it overclocks effortlessly at the stock voltage, without its power consumption increasing a whole lot. $279 may not be cheap for a 7850, but it's definitely not bad for a card that can come so close to the $349 Radeon HD 7870. If it weren't for the (admittedly minor) performance issue we encountered, the 7850 Black would be an Editor's Choice for sure.