how the ballistics compare .451 vs. .458 for long distance (and assuming muzzle fps is similar for similar weight bullets, regardless of diameter-"ish").
Given the same weight, a smaller diameter bullet will have a better Ballistic Coefficient. According to Speer, the BC of the 300 grain .452 Deep Curl is 0.233, and the BC of the 300 grain .458 JHP is 0.204. That difference isn't enough to get excited about.