I think it may be a condenser/diffusion thing. I use a condenser enlarger, and yes, a very thin, boring negative works much better than those dramatic, contrasty ones.

I've yet to do the work of testing for personal film speed, but I have discovered that, for my enlarger, I can reduce dev times by 20-30% from recommended times, and not be hurt in the least. In fact, my usual practice is a 1 stop pull and dramatically reduced dev times.