Nope. HD 4870 actually beats GTX 280 in some cases.
Legion Hardware
And it's very close to GTX 280 in some other cases. So it's a bit in between GTX 260 and GTX 280. GTX 260 overclocked should be able to beat HD 4870, though. But not so much in games. And the risks are... as you know them.
Practically, GTX 260 and HD 4870 should be on the same level, but HD 4870 has an edge on games like GRID and stuffs, and especially with 4x AA or 8x AA.
Heck... I know my HD 4850 didn't even blink with 8x MSAA in GRID. I never knew what AA was like before when I was still using the GeForce 9 series, but now... I know why people are dead-set on getting AA to work.
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