I've got a 16" 6.5 saum and it's one of my handier rifles, especially for hunting in a blind. I run a scenar 123 at 3050 and it smokes stuff. Last year I ran out and went to 130 Berger vldh right at 3k. They don't leave near the exit but seem just as deadly.
I am in the process of building a 30 Nosler 22" barrel for a Nilgai hunt I have scheduled next February. I plan to shoot the 190 scenars in it. I've got a little bedding clean up left to do and it'll be time to start load development. Anymore 22" is about as long of a barrel as I want.
I like speed and will lighten bullet weight to be in the 3k range, I'm off the opinion that is where magic happens
For what you're wanting and asking, I'd pick a short 7mm but a 300wsm is bad medicine too. Good luck!