I run two of these cards in Quad-Crossfire and have continued to be satisfied enough with their performance that I decided to continue using them even after upgrading to a Sandy Bridge CPU/Mobo.
I notice that whenever discussion on these cards come up there are often a lot of misconceptions and outdated information that gets posted.
Drivers. Some claim that these cards no longer benefit from the latest drivers. That is not the case. These cards are capable of using the very latest Catalyst drivers and Caps and benefit greatly from doing so. They clearly benefit even from the latest BF3 and Rage preview drivers.
The last notable driver issue occurred last year. Starting with 10.6 they made changes to the driver that broke the internal crossfire in the 4870x2. Users of these cards stuck with the 10.4 or 10.5 drivers until the problem was addressed directly with the 10.8b and 10.9a hotfix drivers. Starting with 10.10, the fix was integrated in the main driver and there have been no issues since. Even during the gap you could still use the latest Caps on top of the slightly older driver. This, however, occurred during a time when many were already considering replacing their 4870x2 cards, and pushed many to do so. Since those users had already abandoned their cards by the time the hotfixes came, many assume the drivers were never fixed and that you would still be stuck with 10.5 - but that's not the case.
Scaling. Crossfire has improved dramatically in the last 3 years, especially after they began releasing CAPs separate from the main driver. The 4870x2 has benefited from nearly all of these improvements. Unfortunately most reviews of this card date back to when it was released and don't show any of these improvements. Suffice it to say that scaling with these cards is not an issue. In most demanding games I see all 4 of my GPUs at 95%+, I'm not sure what more I could ask for.
DX11 Support. While the 4870x2 is DX10.1 and not DX11, it's important to understand exactly what that means to an end user. What it doesn't do is restrict you from playing a DirectX11 game, in DirectX11.
That is because DirectX11 was built with compatibility in mind and was designed to run directly on DirectX10 and 10.1 hardware. This is accomplished via the concept of feature levels.
So when playing a game in DirectX11, it will first make a quick determination regarding which feature level your card supports after which the game should run normally. You will be running in DirectX11 using Feature Level 10_1, which does restrict you to the DX10.1 feature set, however you still benefit from architectural and efficiency improvements in The DX11 API itself, of which there are quite a bit. As far as being restricted to the DX10.1 feature set is concerned, most would be hard pressed to identify a single visual difference in most situations. The only significant feature you would miss is Tessellation which many disable anyway.
Heat, Noise, & Power consumption
These cards do produce a good amount of heat, but the cooler is easily capable of keeping the GPUs cool as long as you dust at practical intervals. The cards use a ton of power, being one of the only cards that uses more power than a GTX480, which itself is notoriously power hungry.
The cards are certainly not quiet, but they are actually fairly middle-of-the-pack when it comes to noise.
This page has some good info on heat, noise, and power consumption:
http://www.anandtech.com/show/2977/...x-470-6-months-late-was-it-worth-the-wait-/19
I'm not trying to convince you to buy the card, just want you to be able to make an informed decision. IMO it depends on the price more than anything. It has clear negatives in terms of heat output and power consumption but if those aren't of huge concern to you, there is certainly no downside when it comes to performance in the latest games.