I'll second the limb saver butt pad they are the best on the market! But as far a taming a .375 Ultra I not sure if anything but porting it will tame that beast. I think that is a great cartridge though, is your gun a Remington or another brand? I don't own anything bigger than my .300 RUM bought new last spring. But I too would love to own a .375 RUM, and a 338 RUM. Heck since I dreaming, why not own the .7mm RUM as well!
In reality for a 7mm I would like to own a .7mm STW. Sorry I am no help with your question, good luck and keep us posted!