Radeon HD 4870 Game Requirement Analysis
Radeon HD 4870 is a high-end GPU based on the 55nm, third unified shader architecture, R700.
It's based on the RV770 PRO Core and offers 800 Shader Processing Units, 40 TMUs and 16 ROPs a 256-bit memory interface of fast GDDR5. The central unit runs at 750MHz and the memory clock runs at up to 900MHz.
Compared to Radeon HD 4890, it offers slightly less bandwidth (thanks to the higher operating memory clock), the central unit is lower clocked and features twice as less video memory. However, it only consumes up to 150W (40W less). The performance difference between is not very significant and so Radeon HD 4870 might be the best choice, over 4890 since it can be easily overclocked.
Most of today's modern games should run fluently at high settings but with modest resolutions. DirectX 11 games aren't supported.