Most scopes work well on a 416 Rigby or any 40 caliber...Scope problems arise with the 458 Lott and larger bores and most scopes last from 25 to 250 rounds then crash. Add a muzzle brake to the gun and cut that number in half or better, the brake in combo with a big bore is disaster......

The only scope I have found (in 50 years of using most of them) that won't give up the ghost with those big boomers is the Leupold 2.5x compact as its adjustments etc. are in the center of the tube as opposed to the ends...That scope simply works.

On the Ruger No.1 in 416 Rigby and my present No.1 in 416 Rem, I have used a 3x fixed, 1x4 and a 1.5 x 5 varible, all Leupolds and they work fine...

Canjar triggers are the very best of triggers...but a good trigger job is fine for a big bore rifle..

I think your choice of a 2.5x8 is fine but I cannot imagine the need for an 8x scope on a big bore rifle..I have never seen an instance wherein a 2.5x would not have worked on the dangerous game that I have shot with big bores, or for that matter anything else...Jack O'Connor once printed that he felt there was little need for any big game scope over 4x..I agree with him 100%...