Now I imagine this varies from club to club, but generally.... if I put in a titanium high torque rotor in a 21.5 stock class --- BUT the rotor is roar approved for stock racing... is that OK?

Like I said I'm sure it depends on the club, but is it generally accepted and most fast guys do it? Or would it be frowned upon?

Theres 2 types of 21.5 classes really. Ones that run some sort of limited motor setup, including timing gearing rotor etc. Or just a "21.5" class where anything goes as long as its a 21.5.

Like you said, depends on the track. 2 tracks I know use different motors.

If you're going to be that concerned about power....just run 17.5....

ask the td if they will have a issue with your plan. all tracks vary