OK, so my system used to be Vista 32 bit with 4GB RAM and otherwise same specs as now (which see). Before I had no real probs with stuttering. Now with 6GB RAM and Vista 64, same settings in-game I'm getting occasional stutters- but around 1 second stutters that effectively ruin my race. This may happen it may not and there seems to be no rhyme or reason. Sometimes i can run a whole race with np. It's happened offline and online (online seems worse).