I'm assuming you are from Canada because we don't get a whole lot of Ross's down in the lower 48 and the hex 91/30s are a bit of a rarity in recent months.
all three would be more than enough to kill a deer, but from my meager understanding of the ross, it was a great target rifle but performed poorly under adverse conditions. it may not perform well if you are hunting in extreme cold like I've been doing the last 3 days(-7 farenheit yesterday morning here in the mountains of Idaho). same might be said for if you are hunting sandy or dusty environs. the 91/30 and number 4 MK1 would be much more reliable, I believe that the Canadian Rangers still issue the number 4 in the far north so I'm thinking it would be great in cold weather, though the 91/30 has served in some of the nastiest cold weather combat zones of the early 20th century. you really couldn't go wrong with either, but the number 4 is a much nicer rifle for the job in my opinion. it's shorter, better balanced, less cracks and gaps everywhere, and generally speaking more accurate.