I have a MKII with the 22" barrel. The gun fits me perfectly and balances great. I don't think I would want any longer barrel for this rifle.
I've tried numerous loads in mine. Here are my results. All bullets were loaded over RL19. 57gr seemed to be the magic number for all bullets. It's a max load, but my gun seems to like them better.
140gr Gamekings: Shot awesome. Tied for most accurate bullet out of this gun. Problem was it was just too explosive on deer. Out of 20+ deer, I had one pass thru. Most of these weren't shoulder or frontal shots either, they were broadside shots. I finally gave up after the last doe I shot with them kept going after 4 shots. I later found that the bullets splashed under the hide and failed to penetrate. They only slowed here down.
140gr Nosler Accubond: Another accurate bullet. Good expansion whether it be bone or broadside. Most consistent bullet I found. I would highly recommend.
140gr Nosler Ballistic Tip: Accurate. Too explosive for me. No pass thrus on 3 deer shot broadside. They were a mess inside, but still no pass thru so a nogo for me. Heavier and maybe slower loads might have worked better.
139gr Hornady GMX: I haven't tried these out on deer yet, but wow, awesome accuracy. Could believe the first 2 three round groups, .45" & .6" center to center. Plus, I picked up 150 of these for $40 shipped! Can't wait to see how they do on deer.