Great question - haven't figured that out yet - I'm guessing 40 or so? My 1720 with the same reg gets at least 80 or so with a 13 ci/3000 psi bottle.
I've been wrestling an issue with paintball regs, and finally decided to use the one on the gun now. For some reason I can't get over 12 fpe with an 1800 psi output reg that I know works correctly after confirming on another tube with pressure gauge.
It maybe a weird combination of tube length versus available plenum? Non linear/diminished return results drive me bonkers, but I decided to just go with the 1500 psi reg, as I knew it would give me decent power above 12 fpe.