The Radeon HD 5870 Eyefinity6 distinguishes itself from the vanilla Radeon HD 5870 by sporting 2GB of video memory, six Mini DisplayPort outputs, and the clever use of superscript. AMD cited a suggested e-tail price of $479 for this beast upon its introduction, but most current listings at Newegg are at $499.
The tentacles on our card, shown above, are Mini DisplayPort-to-DisplayPort adapters, which you'll probably need, since Mini DisplayPort isn't especially common. AMD says these cards ship with a total of five adapters to get you started, including two Mini DP-to-DP cables, two Mini DP-to-DVI, and one Mini DP-to-HDMI.
All of those adapters are of the passive variety, which means they're simple plug converters. That's fine for most uses, but the DVI and HDMI connectors are limited to a peak resolution of 1920x1200. If you want to drive a higher resolution display off this card via HDMI or dual-link DVI, you'll need an active converter, which is a more expensive proposition. AMD keeps a list of Mini DisplayPort adapters it has validated for use with Eyefinity, and I can find only two active adapters on it at present, one HDMI and one DVI. Both are made by Accel, and either one will set you back about $110 at Amazon. Additional passive adapters are much less expensive, ranging from about 15 to 20 bucks.
Incidentally, that means you can tack another $60 on the total cost of a six-display setup, since you'll need four additional Mini DP-to-DP converters to make it happen.
Another way the Eyefinity6 card differs from the plain 5870 is the conversion of one of its two six-pin aux power plugs into an eight-pin variety. AMD tells us the card draws more power when driving a full complement of monitors, necessitating the change. That little move is noteworthy, too, because you may have to buy a better class of PSU for a system hosting this video card.
Although the Eyefinity6 edition's clock speeds aren't any higher than stock, the addition of a second gig of memory ought to help performance in high-megapixel situations where 1GB just isn't enough. We saw in our GeForce GTX 480 review that the step up to 2GB simply didn't buy you much on a 30" panel, but for six megapixels or better, it's probably a requirement to ensure smooth gameplay. What's shocking is how often a single Eyefinity6 card with 2GB of video memory delivers quite acceptable performance at six to 12 megapixels, without requiring major compromises on image quality. This age of Xbox 360 ports has led to an embarrassment of riches for PC graphics chips. (Again, you can see those wheels turning.)
In the event that you would like higher performance, there's the option of going to a multi-GPU CrossFire configuration, although, like everything else in this realm, doing so requires navigating a minefield of limitations. For one thing, you'll need a second Radeon HD 5870 card with 2GB of RAM. Add in a 1GB card, and the CrossFire pair's effective memory size will be reduced to the lowest common denominator. We tried such a configuration briefly at one point, and CrossFire team was sometimes slower than a single GPU with 2GB of RAM. Not advised.
Happily, we had a solution on hand in the form of this Asus 5870 Matrix Platinum card, which has 2GB of GDDR5 memory onboardalong with a slightly juiced up core clock and hooks for overvolting and overclocking. Using this card alongside the Eyefinity6 edition produces a proper 2GB CrossFire pairing.
Don't think the additional video outputs on that second video card will allow you to hook up more monitors, though. All of the displays must be connected to the primary card in a CrossFire team.
Also, don't expect the same sort of performance scaling you might see from a CrossFire setup on a single monitor. The frames generated by the secondary GPU must be forwarded to the primary card for display. Normally, that data is transferred over the CrossFire link provided by the bridge connector between the cards. However, that link's bandwidth is only sufficient for resolutions up to four megapixels. Go beyond that, as you would in nearly any conventional triple-display setup, and the frames must be passed from the secondary GPU to the primary via PCI Express. Two GPUs will still generally be faster than one via this arrangement, but performance won't scale quite as nicely as it does in single-display setups.