From all the reviews, it seems as if it eeks past the 275 in performance, and seems to even exchange blows with the 285, up to 1920x1200. Wicked. Since I sent my other 4870 that I was using for crossfire back, I think I'll get this. Love that you can OC it past 1ghz, even MILD ocs on the 4870 showed great performance increases, memory...not so much since it already has a huge bandwidth, core OC is where it's at.
On topic of the 4870 2GB, from what I saw it did virtually nothing...apparently it has all the memory it needs at 1GB, the core-clock increases are what show a huge difference if you look at the OC marks, the 4870 1GB oced to 800mhz, is right on par with the 4870 2GB at 800 mhz, so it's all about the core, there was maybe give or take, a 1-2 fps difference, not worth it IMO. I guess it's no different than when you look at benchmarks with crossfired 1gb 4870s, and a 4870x2 with 2gb, crossfireing 4870s, does not make increase it to 2gb, it is still 1gb, yet the 4870 crossfired, running at 1gb, beat out the 4870x2. So I don't think memory is a big factor here.
And there's no way that Sapphire 4870 can OC as much as the 4890, way to many improvements on the 4890, as even they say. Plenty of people are hitting 1GHZ with stock cooling, I wouldn't dare try that on a 4870, even with aftermarket cooling. I even underestimated this card thinking it was just a highly over-clocked 4870, but they replaced the PCB, and made loads of changes that drastically improved the card. Props to ATI, they went on a build that was solid and proven, and made it even better.
Just an FYI, got the Accelero S1 and 4890, got it to 1ghz, with NO volt mods. Capicators are a bit loud off the bat, seems all these new "larger" caps are :-\, can't hear 'em when gaming w\ headphones though .