RE: Scope Size
What flavor suits your taste/usage best(2x7, 3x9,etc)but I think 2x (lowest) and 10x(highest) are all that required on a big game rifle.
40mm- 44mmobjective
The best you can afford( elite 3200, FFII, etc is my min suggestion for a CF for biggame hunting - if you can't afford 200 dollars buy a cheaper rifle or save! I have seen guys drop 1000 on a rifle then skimp the scope and rings b/c they spent the wad already. It makes absolutely no sense to me, as I'd much rather have a 500 dollar rifle and 500 scope instead)
Quality ring and bases - I will not use alum bases on anything other then a rimfire so that pretty much takes care of all the cheapie's and a good portion of the ever popular weavers as well. I personally like Leupold Double Dovetails or Warne Maxima's.