I did a quick search to see if someone else hasn't reported this yet, but if I missed it, apologies to all.
With overdrive on, even extremely simple patches give me terrible timing issues. (See the self-explanatory screen grabs.) Essentially, [timer] reports [metro 200] intervals of 200 ms while [cpuclock] measures around 440 ms, with overdrive and msp on. (cpuclock is right.)
Driver: CoreAudio EDIROL FA-101
I/O Vector size: 512
Signal Vector Size: 64
Scheduler in overdrive: check
Audio interupt: check
Vector optimization: check
Note that settings audio driver to built-in output solves the problem, as does setting scheduler off the overdrive or the audio interupt.