My 6.5WSM is almost complete, i'm running a 30" Obermeyer with a Stiller S/A (i'm going to be rolling single shot with this one).
the 6.5RSAUM has a few advantages over the WSM:
With the reduced powder capacity, the RSAUM brass is better suited to the 6.5 bore (the WSM is severely overbore) & with Lapua beginning 7mmRSAUM brass production
, I would have gone with the RSAUM in a heartbeat.
The RSAUM will meet the velocities of the larger WSM with less powder & also do so with increased bbl life (how much I can't say).
I vote for the RSAUM,
PS- you don't have to buy a new bolt if you don't want to, your 'smith can open the bolt face. The caveat being, depending on what your 'smith charges, it's usually a fairly negligible cost difference to order a new one piece PTG bolt with a better extractor, they usually fit better in your action as well.