Cheers TheMantis,
I think i've sorted it, I rebooted to safemode, uninstalled everything nvidia and ran a driver cleaner to get rid of any traces left, then restarted and put the latest 190.62 WHQL's on ... now it runs fine.
Must have just been some holdover from an old driver revision in there, I've had this install over 2 years now.
The fun will begin again on Friday, i've decided to go Solid State Drive with Windows 7 (fed up of the loading times), but tonight has given me hope it'll run well on a clean system.