That load oughtta rock back a little.
I just bought a SBH 4.62" and was wondering what to expect from it, velocity-wise.
Are you using a 1.610" OAL or longer?
Chronoing the same load in a 7 1/2" and 4 5/8" SBH I found the shorter barrel was 100 fps slower. That is what I'd expect, but due to differences in cylinder/barrel gaps, throats, et al, velocities can easily vary +/- 50 fps from nominal velocities for a given barrel.
Hence a "fast" 4 5/8" could produce the same velocity as a "slow" 7 1/2".
All that said, it should be no problem pushing 300-320 gr cast 1200 fps in a 4 5/8" sbh, if you add a bit more fuel 1300 fps is easily achieved.
