The blackheart tops out at 20 bps, if you want it for fun (don't we all)...the virtue, doesn't.
Ideally you need to upgrade the internals of the gun to allow it to go faster...QEV is a good idea, as it will allow the marker to cycle at 26 bps, subject to board and other components.
Lucky internals are a very good idea, stages 1-3, virtue board and QEV...machine gun.