I think your better off with a wsm, I think they're more efficient with a shorter barrel. I'm working up a load in my 17.5'' 7wsm with r17 and a 168smk. I'm at 2850fps with no pressure signs at all... my buddy has a 300wsm in the works, should be pretty sweet with a 18'' barrel.
I have a 18in Encore barrel plus JP brake, I only have about 250 rds down the tube. This length barrel seems to work great for me. I have only shot the Sierra 165 SPBT hunting bullet and the Sierra 190 gr MK, both seem to work in a 18 in barrel using IMR 4350. Have fun.