Need a suggestion.

I will uograde my pc soon.But I can't decide the graphics card.Sapphire Radeon HD4850 512MB or Sapphire Radeon HD4870 512MB?I have seen in reviews that HD4850 runs everygame at veyr high settings except Crysis and Crysis:Warhead.But I will have to consider my budget also.I have seen in some videos of youtube.com that Crysis and Crysis:Warhead gets 30FPS with very high setting on Sapphire Radeon HD4850 512MB at 1280X1024 resolution.I will be able to play games at highest 1280X124 resolution beacause my monitor is 17".My question is if I get a Sapphire Radeon HD4850 512MB graphics card and set all settings to very high on Crysis and Crysis:Warhead and set the resolution to 800X600 will I get more speed than 1280X1024 resolution?If anyone has a Radeon HD4850 512MB please test with all settings to very high at 800X600 resolution.On the other hand Raeon HD4870 512MB run the games smoothly with all set to very high at 1280X1024 resolution.PLease test and tell me.