I own a custom long barreled 270wsm and a short light 300wsm. I'm not convinced, as yet, of any advantage in the 325wsm over the 300wsm. It is a very interesting round and from the stats looks like it would be as effective as the 338wm with 225gr and lighter.
Anything lighter than 225gr in the 325wsm. I would prefer the 300wsm with 180's. Anything larger than 225gr in the 325wsm. I would prefer the 338wm with 250's.
In other words. If you held it to the 225gr. The 325wsm would be a fine choice.
Yes there is load data for the 300wsm in bullet weights heavier than 180grs. The situation that arises is the length of the 200's and 220's seats the bullet deep into the case. Thus cutting down on performance and the 180's out perform the heavier bullets.
From my experience with loading for the wsm's. For big game, I would recommend either the 270wsm with 140's. The 300wsm with 180's or the 325wsm with 225's. Any of these would be devastating on game.
My 270wsm like 130gr Hornady Interbonds and 140gr Nosler Accubonds. My 300wsm likes 165gr Hornady Interbonds and 180gr Nosler Accubonds. If I were to load for the 325wsm. My first choice would be the 225gr Accubond (If they make it) nothing lighter and nothing heavier.