All of this is hearsay. So is a 1-7.5 too fast for a 6.5cm with a MV around 2675-2700?Too fast? Never heard of such a thing.
Is there any calculations for that? What kind of speed difference would one expect from 1-8 to a 1-7.5? Would probably want to run 140 or 147eldm out of a creedmoor.Short answer- no.
That said, shorter means reduced velocity, so to combat that you'll likely want more powder with lighter pills…and you don't need faster twist for lighter pills. But it won't hurt anything.