In this article, iXBTlabs is trying to find out what graphics card to choose, if you have about $300 to spend and cannot afford a High-End product for $500 or more. Here's a bit:

The overhauled GeForce GTX 260 outperforms its rivals noticeably (given the prices are similar). There are some exceptions, of course. Perhaps, performance ratings may change with the release of new drivers. But on the whole we admit that NVIDIA GeForce GTX 260 is the best choice for the 300-dollar budget.

As for frequencies, there have already appeared overclocked modifications of both 4870 and GTX 260 cards. So it makes no sense to consider frequencies alone. Besides, don't forget that GeForce cards offer more performance per 1 MHz.

HIS IceQ4 RADEON HD 4870 Turbo 1024MB is an excellent product with a noiseless and efficient cooling system and a good bundle (with a bonus even). As for the competition with GeForce cards, prices decide everything here. If this card is cheaper, it's a success.

PALIT RADEON HD 4870 Sonic 1024MB offers an interesting range of connectors for any monitor, but it lacks a TV-out. Its cooler is also efficient. The bundle is rather mediocre. The final decision also depends on prices.

As for performance differences between 512MB and 1024MB editions of RADEON HD 4870, we have already analyzed this issue and haven't found any differences, except for several games.