you will need to be carefull with some graphics cards as the game may say it supports them but infact you get really poor performance. Only way i can get the game to run is through the no dvd crack otherwise its runs like a pig. As for recommendations, i use ATI 9200 512mb and it runs sweet.
the 6800, isnt quite as good as the ati x800 series, you put AA and AF on a 6800 and it struggles, on an x800 it handles it very well, wouldnt base you choice just based on PES, as its not a demanding game, look at other games you want to play as well, then make your choice.
I have an Nvidia Gforce 5200Fx and it works Fine, also i have the Nvidia Gforce 6600GT loadmixer everything on best resolution, works perfekt! but only with the NoCD Crack, otherwise stuttering with both cards!!!