Just a small additional point which maybe trivial ...
When I'm setting up my pcps I tend to set them to be doing @ 770fps with 8.4gr. They can actually do just over 800fps and be legal in the UK ... but I always seem to have them at 770fps which is @ 11fp.
When I set up the 10.6gr because they are the heaviest I have I set them so the top of the spread was virtually on the 12fp. So they were doing @710fps.
So they have actually stolen or recovered @30fps MV in the equation off the 8.4's anyway, which may be worth a few yards over the range.
Worth noting if you are looking on Chairgun and changing weights and BC but keeping power the same.