I've been having a fair bit of trouble
Been getting some stuttering and jerkiness lately with some mods & tracks, been blaming the tracks
Then I noticed stuttering even on tracks & mods I've had no troubles on before.. I tend to update my nvidia drivers regularly
After much stuffing around, and a bunch of testing, including stopping all unneccessary services in the background to make sure its not a background thing causing me issues - the way I've managed to get back to smooth gameplay & get rid of the stuttering/jerkiness on even the worst tracks & mods is by going right back to 197.45 release drivers..
I dunno what nvidia are doing with the 2xx series drivers but they aren't good for me
Thought I'd post in case others are having similar issues - try going right back to 197.45
Basic Specs
Win7 Pro 64bit
Gigabyte GTX 275
Gigabyte P55 UD4P
Intel I5 750, 8GB Mem, 1TB HDD
EDIT: Frame rates are "OK" with 2xx series drivers, at least 60fps at the lowest point and generally running much higher (often well over 200fps) and the fps i similar with the 197.45 drivers so it's not a performance issue I'm seeing with the 2xx series, it's a straight up jerkiness/stuttering issue that isn;t there with 197.45