GAP is starting to tout the 6.5SAUM on SnipersHide pretty well. Even talking about a special rifle package just for that cartridge. Brass availability is going to be the real challenge
I have the WSM, shooting 130 CEB's @ 3400fps with 3/8" 5-shot 100yd groups. I highly doubt that a Berger will ever grace the bbl of this 6.5 as it is a hunting rifle & from what I've read, the Hunting VLD's probably won't hold up to the velocity.
I do think the SAUM will be more efficient & do pretty much everything the WSM will do, I didn't know that when I built my WSM. But i'm happy so, I get a little more horsepower & brass is almost plentiful.