MOTUnation.com

I am working with some tunes that I'm still trying to find the right tempos. I have audio files (scratch vocals and guitars) and I'm wanting to try about 3 different tempos to send to the client to see which fits.

Is there a quality difference between using SCALE TEMPO vs ADJUST SOUNDBITES TO SEQUENCE TEMPO?

I'm basically copy pasting into new chunks and using different tempos in the sequences and want the audio to stretch or squeeze to fit the tempo set.

I think it's the same algorithm, which, by today's standards, is not very good IMO.

If you have MachFive you should probably do it there instead. It's really MUCH better.
Otherwise, you can also try Amazing Slow Downer, or even Apple's AU little plug (which you already have).

I do have M5 but haven't used it yet. I'll look for some tutorials on how to get into M5 deeply.

This should get you started:
http://www.groove3.com/str/machfive-3-explained.html

You can even jump to the relevant section just to learn how to do what you want in MF (the ICRAM granular synthesis). Eli will take you step by step. Very cool!