Ken, what did the .458 weigh?
Most doubles are built to correct weight in the first place, whereas bolt-guns can be fitted with plastic stocks and without scope may weigh only 8 to 8 1/2 pounds. They DO need taming, though the recoil is not so noticable in the excitement of a DG hunt of course.
Add an extra pound or 2 with the reducer by all means, won't stuff up the handling of a bolt-gun much.