Yep, you'll gain enough to take advantage of newer powders, & not be running compressed loads.
As long as its throated long, & has a long enough pipe.
*but, you could always do the same thing to a 300 Win & beat the WSM again because of the larger case capacity.
In the end both cartridges absolutely kick @$$!
I built my 300 WSM
on a long action Model-70 Win, with a 26" flited #4 Hart 10 twist.
It beats my factory 24" piped 300Wby hands down for velocity.
* but again, to be fair, if my 300Wby had a longer pipe, (optimal length to take advantage of the case capacity) it'd win the race between the two, due to the larger case capacity of the Wby.
It's an Apples to Oranges comparison.
A hot rod WSM on a long action, is given all the advantages, vs a factory rifle in a standard magnum chambering, is basically handicapped in comparison.
To be fair, you'd need to compare optimal to optimal barrel lengths, mag length, throats, etc. then it flip flops the discussion.
If I had mine to do again, I'd still go with the long action WSM just cause I like it. Not to mention a 180 Accubond, over 3,100 fps with only 65.0 gr of RL-17 is just plain SEXY! (*Alliants recomended MAX of 66.0 gr of RL-17 was doable, but a ill too hot for decent brass life*)