I've got a Christensen and a custom both in 28. A friend of mine shoots the same Christensen in a 300 RUM and it has much more recoil. Stick with the 28. Also, I've had great luck with the nosler 175gr long range factory ammo. Shoots well out of both guns.
I'd mix up baking soda to toothpaste consistency and spread it all over the skull and put it into a sealed plastic bag. Give it a few days for the concoction to fully dry and hose it off. That's how fat and grease is drawn out of granite.
Marshland Outfitters in Saskatchewan. Big bear and tons of color phase. I've hunted with them a couple of times and don't have a bad thing to say. Great accommodations and a no nonsense operation.
I'd suggest a gaited horse that has a strong field trial background. They've typically seen a parts of the country including mountains, desert, thick timber and prairie. They're comfortable around gun shots and are often snack broke. Try to find one that a professional field trial trainer has...
I deal with warranty contracts as part of my job. Send Outdoorsman an email detailing how you'd like to correct the problem. They'll either approve it, deny it or ask you to do it a different way. Stick with what they ask and keep everything in writing.
Don't over think the turret. In my opinion, the altitude is the least of your issues. Be confident in your shooting and practice long range often and give them hell. You'll never make the shot you don't take...