My System: i7 6700k, 16gb ram, SSD drive and Windows 10 64bit.
starting two clean empty projects, one time in 8.5 the other in 9.0.20 - same system.
adding one track with a vst 64bit synth (xfer serum)
start playing notes
behaviour 1 in 9.0.20: cpu spikes which lead to stutter in sound
behaviour 2 in 8.5: everythings fine
same system, same synth, same preset.
9.0.20 has some serious issues - I hope Steinberg already knows them.
As a technical consultant I offered Steinberg MANY times to be a beta tester to help them out, but they are just ignorant.
So my feelings for Cubase fall from day to day, as I cant use version 9 since release (first the audio warp issue which is a biggie for me… now this cpu spikes…)