All HQ modes are the same data rate, 35mbps.
Overcrank is a higher data rate.
[Enrique Orozco]"does anybody have compared slow-mo in software (with 60p files) vs. 30p overcranking (I know, with SxS) ?? "
Do you mean changing 60p to 30p at half speed. I haven't tried this myself but if you use something like Cinema Tools which is just changing the "flag" you should be ok. What you want to avoid is creating frames where there were none as in "typical" NLE slow mos. Even Optical Flow will not be as good as playing back frames shot in camera generally.