No, never tried 450s.

Based upon my testing years ago using LR regular versus magnum primers for my hunting rifles in cold weather below 25 deg F, all I could see is that the magnums increased velocity by about 12 to 15 feet per second and didn't change the POI.
Since I was happy with the BR-4 performance versus the CCI 400s, I never thought a change to a non-benchrest magnum primer would have necessarily improved accuracy.