When you're in a ASW-20C @9lbs on tow and you feel like you are always about to stall on tow, that is too Frikkin slow. Yes, been there done that, feigned an issue so I didn't end up behind that tug later in the contest when wet.

Speed in thermal? Sorta depends on if smooth or rough, I don't know, what feels good? As AOA goes up, some airspeeds lose accuracy. If the plane feels happy, then I'm happy.
I'm too busy watching for other traffic and rely on sound and feel, not looking at an instrument that is a second or two behind actual.