I think i sorted my probs out. I installed the latest Nvidia 178.13 WHQL drivers, after removing the old ones. Ran 'driver-sweeper' too and found old traces of NVidia (and ATI ..despite never even owning an ATI card !) and ran Disk-Keeper a couple of times afterwards as SP3 had fragged my system and game files all over the shop...cant think why i got bad stutters during the race
Then installed Riva tuner for first time to do some gfx tweaking and overclocking.
All appears to be sweet and merry now...so far!