We have a 727cc, a 760cc and 845cc motors.
727cc: is a ported 61x cyl with enlarged exhaust ports, and cleaned up transfers. 33cc domes, about 210 psi compression. Has epic, Bpipe, single 48BJ.
760cc: ported 64x cyl, ported, compression around 185psi, dual 44mm, MSD TL.
845cc: maxx sleeves, cr500 pistons, rest of setup as above for the 760cc.
Comparison:
responsiveness feels very goon on all skis, however there is a considerable difference from the 727cc to 760cc. The 845 feels a bit stroneger that the 760, but only by a small bit (probably more torque, not power as such).
To make this fair, I must say the epic was not fine tuned, and the 727cc has oem flywheel, the other setups use the power and weight of the MSD wheel and system.
To be honest, if I port the cases and fine tune the ignition and water and pump I can get close to the 760 power range. That said a 760 seems to be the best in terms of power/cost. Later go big at least 900-1000cc range. The 727-845 cc are super reliable except the crappy MSD switches and connecteros that take in moisture and cause problems.