Fuj, an interesting area to explore. Not sure anyone has really done all the work.

Historically cast bullets are shot at slower velocities for a few reasons. Initially barrel leading was a problem, but, current lubes and gas checks have been successful up to around 2600fps (in .30cal). Then there were the guns. Most are made with rifling twist for jacketed bullets, which means the RPM is limited, which means the vel is limited. Again, some have experimented with slower twists and reached higher velocities.

If it were me I would think a higher vel would be better, just for wind effects. Not sure where that optimal vel would be with a light bullet. If you look at the BR shooters the 30cal bullet weights vary from 130 to 230gn. Most seem to keep the vel in the 1500-2000fps range. Why? Don't know. I suspect the ones using heavier bullets do so to reduce the wind effect, but, again I am just speculating.

I would be very interested in someone pushing some of those boundaries. :)