I don't think any of the benchmarks I've seen compare them directly, but you could also just look up specific games benchmarks for GT's in SLI vs the brand new 4870 reviews coming out today.
I would think the 4870 is the best buy if you're buying new; that way you can add a second one down the road during a big sale like Boxing week or something. You can also go with an Intel chipset that way!
#2) But the difference almost becomes zero when AA is turned on.
There aren't any direct benchies for 8800GT SLI vs 4870 with AA on.... but since SLI 8800GT is virtually 9800GX2 .... this will give you an idea of point # 2.
The difference is almost nil at low res...but its another story at high res. You will notice that 9800GX2 gets its arse beaten by a 4870 at 1920 with 4AA.
2 8800GT in SLI beats the GTX 280 in almost every game and it actualy performs like a 9800GX2
So i say go for 2 8800GT in SLI unless u play @ a resolution like 1024x768 which doesn't benefit from SLI
im not sure about how loud it is if there are 2 of them HD4870. but its definately hot as 90C+ when in case. review done on open platform achieve something in the 80C's.
and btw monsta. who cares if it runs hot (5 c higher than gtx card) its covered by a lifetime warranty so i dont think amd would offer that if there was a problem. You can always wait for partners to come out with 4850s with aftermarket coolers which will run incredibly cool and extremely overclockable
get 2x 4850s in crossfire. it will smoke ur current setup out of the water in every game
You are with the guy who has 2 8800GT ? if so then u are wrong, because although HD 4850 is better than a 8800GT but the difference isn't worth the upgrade