I have been out of the game for a while

Most people prefer XP for responsiveness, not so much in games, but out - the rest of the OS is a lot quicker than Vista, plus it uses less memory.
As for the 4870s, it's not just a little extra money, it's an extra £125 if you're buying two cards... no small sum when even two 4850s can max every game out there except crysis at 2560x1600!

 

IMO i have been running vista for a year now, and i cannto go back to xp. xp is sluggish in comparison (yeah i know, i jsut said that :O )

and yes vista uses more ram, but is ram nto there to use? AND if anythign with more priority needs the ram (eg games) the pages are swapped from system processes to swtiching pages to and from the gpu RAM and desktop RAM. its memory management is a hell alot better than XP.