I'll tell you what...the new centerfeeds feed awesome. If I was going to do it again, I would do exactly what I did, and not change anything. It will hold 3 rounds and cycles flawlessly. I love the extra "HorsePower" of the 7 ultra over the 7WSM. If you did want to go the WSM route, I would go with a long action. Here is a pic I took for you with one of the new centerfeed long action, DBM with a 300 WSM cartridge loaded to give you an idea. Next too it is a 7 ultra.
Mcmillan will inlet an A-5 for the detachable mag set-up. I have some bottom metal, trigger guard, and magazine, I'll let go cheap if you are interested. I have a 300 WSM large shank 12 twist 3 groove, waiting on an action. I plan on using it as my "woods" gun where shots will be shorter.
I will say this building the savages over the last 5 years has become addicting. I've been shopping lathes and plan on putting one in my gun room soon to continue to feed the habit!