Depends on the resolution, I'm supposing 20" is 1680 x 1050. If so, it should be able to max out the majority of modern titles, however, there are several exceptions, the typical games such as Crysis Warhead, Metro 2033 (even an HD 5870 struggles to play Metro 2033 at 1680 x 1050) & Shattered Horizon - the main three I can think of.