I run a 26" bl. on my .375/06IMP and get 2,470fps with all the 300gr., and 2,650fps with 270gr. TSX. Love it and don't mind the length.

My old .375/06IMP at 22", did just fine and was not quite 100fps lower speed - different barrels give different speeds with identical loads.

You won't know until you chronograph it.

The .375 H&H developed it's fame with a 300gr. at factory speeds, 300gr. at 2,400fps and 270's at 2,600fps - just what the speeds were out of hunting rifles, don't know, but they'd be less than these "published speeds", usually taken from 28" bls in 1912., iirc?