Have thought about this one a fair bit. I've had shorty 270, 7, and 300 wsm rifles over the last 10 years. Shorty 7 was first, that was when the 7 saum was fairly new and hadn't been adopted like it was now. Was 7 wsm with winchester and 7 rsaum with r and p... and the wsm had more boiler room. Looking at brass options, 7 saum would be the logical choice now even given its capacity loss to the wsm.
All that said, if I could locate and workup several hundred winchester pieces the wsm has boiler room going for it. Reality is both are 3 down at best and a little more scoot is always nice. Both probably benefit from xm actions with the super sleek pills.
I'd be hard pressed to jump on the 280 band wagon in a 20 inch barrel. The marketing hype about usable barrel length seems more important/valid as barrel length decreases. I've had both shorty 7 wsm and 7 rum rifles. The rum still handily out ran the wsm (30 grains is 30 grains) but the wsm lost a lot less from 26. I'd be hard pressed to do anything long action in a 20 inch barrel (although my current main squeeze is a 21 inch 7 rum... making me a hypocrite), ruling out the 280ai.
My money being spent, probably going to be 7 saum...
