R8 have put another update up last night, as the frame rate on 3 of the tracks had dropped on my i7 / GTX970 / 32gb ram PC from 135 FPS down to 35 FPS.
Some people couldn't get it to run at all, seems R8 new what the problem was once about 10 suffering the same thing posted at the FF forum explaining what was happening.

As for the stutter, I might of noticed it on a previous build, Niagara track I think, as that is the flattest and it would be the most noticeable on that, but this current build seems OK on the tracks that haven't suffered the frame rate drop...... I haven't had enough time on the MK2 version of this current build, as it was 3.30am when I installed it, and I had to go to bed so I could get at least some sleep before heading off to work.