For the best gaming performance you want Win XP because DX10 and DX11 effects are more demanding. Additionally, the OS itself uses few resources.
However, DX9 support is starting to be dropped. Just Cause 2 is one of a handful of games which cannot be played in Win XP. Similar to how Oblivion marked the end to DX8 support. I figure in 2 or 3 years most or all new games will drop DX9 support.
Win 7 Home 64-bit is the safe way to go and you can always play games in DX9 mode so that DX10 and DX11 effects are not used to increase performance. Unless of course the game you play requires DX10 or DX11 like Just Cause 2.
hello...i hv recently upgraded my PC to i5 2310 2.9Gz with Intel Original Motherboard.....4gb Ram....Nvidea 9500GT....i hv been tryin for win xp 32bit....bt its nt supporting my system !!! i hv tried out 3-4 XPs bt in vain !! now running win7 64bit....its running fine bt actually i need to play the game The Witcher 2 which is nt compatible wid win 7.....so i need xp.....wat to do ?? does i3 supports win xp or if u kno any i5 processors dat will support xp ??