I have a 340 Wby in a Sako Finnbear. It is a 1-12" twist so not the same as the Mark V. I found that it shoots the 225s the best but I typically shoot 250s in it. The 250 grain Berger is a game-slayer for sure! The lighter constructed 225s are not very good for some game- they really come apart on impact.
For powders, I like R19 for 225s and N560 and Mag Pro for the 250s. R17 works well too. I can get 3000 fps easily with 250s in my barrel (26" Gary Schneider ). Mag Pro, Magnum and R17 get there.
For recoil, I just shove a 8x10" piece of woolskin under my shirt or jacket. Make sure your scope has plenty of eye relief. It is a scope killer though. I have ruined 3 or 4 scopes on it so far.
