Several questions on this topic:
What is the case capacity of the 7mm SAUM?
Do people use it as parent for wildcats?
I was thinking of a 6.5 Rem SAUM vs 6.5 284, would it be more efficient?

John Barsness addressed that very topic in the latest Rifle. The 7 SAUM capacity is very similar to the .280 Ackley improved. If you expect 6.5 Ack Imp ballistics from a 6.5 SAUM, you shouldn't be disappointed.

Capacity is just a slight bit more than the 6.5 Rem mag.

BigIron

By "6.5 Ack Imp ballistics" do you mean 6.5'06 Ackley Improved?