The 168 Nos BT is more than adequate for Dall sheep, I've shot and have been associated with the taking of more than 20 Dalls over the years. They are one of the most fragile of all natures big game animals.
Unless you are doing a life size mount, just shoot him behind or on the shoulder and don't worry about cape damage, that's for taxidermists to worry about.
If you do get blood on the part of the cape you need for your mount, remove it immediately with cold water and a spoon, working the blood out of the hollow hair until it's clean. This must happen as soon as possible before the blood dries or your sheep will have brown blotches on him. Once the blood dries there is no way to get it out and even bleaching by the taxidermist will only make it light brown.
350 mtrs is a vey realistic practice range for Dall hunting, the further you can shoot effectively the better your chances of a larger ram. You can't always get within 200 mtrs and to have to walk away from a 40" ram because you can't get closer than 400 mtrs without spooking them would really suck, in my opinion, and it can happen. With practice, 400 mtrs is not difficult and is very doable with an '06 and a range finder.
Go buy yourself 20 boxes of the ammo that you intend to hunt with and go to the range every opportunity and practice. By the time your hunt comes along you should only have 1 box of ammo left for the hunt, and you should only need 1 round for that. Do not make the mistake of practicing long range shooting with cheap ammo and then just resight for the hunt, it don't work that way. Shoot the ammo that you intend to hunt with, if you can afford an outfitted Dall hunt you can afford a few hundred or even a thousand dollars for ammo.
Just the opinion of an old sheep killer.
Douglas