I have yet to find an effective way to sync audi to midi other than either creating the midi & adjusting the tempo before you cut the audio track.
I think the best rule of thumb is a scenario like this:
Create a midi or click track and adjust the tempo (bpm) to the tempo you would like your audio performance to be performed at.
Cut your audio.
Never cut audio without playing to at least a click track at the appropriate BPM.
I hope this helps