Conventional wisdom from as far back as the '50s, I think, brackets the fast end as IMR 3031. That one's okay, don't go faster unless you're willing to get slower velocities with safe loads. High port pressure is NOT a problem with "too-fast" powders, but I've never heard/read/seen/experienced any firsthand reports of port pressure being too low.
Well, my lead-bullet loads with IMR 4759 didn't cycle, but we didn't expect them to. Those were way-light anyway.