I am converting my lathe to have a VFD speed control. The motor in it now is a 2 speed import rated 3 or 4 HP depending on speed selection. It is rated 1725/3450 RPM. I plan to replace it with a 7.5 HP single speed, inverter-grade motor. I want to have good low-speed torque so it is over-sized. There seem to be more choices in 1800 RPM motors vs. 3600 RPM motors. I have room to change the pulley to a larger pulley and use the lower RPM motor. I have to change the pulley anyway because NEMA motor shafts don't come in the Chinese /non-NEMA diameter that this one has. Would you: Change the pulley diameter and maybe (3) belts and use 1800 RPM or use the same diameter pulley? Anyone think of an advantage one way or the other? Cost difference would probably be a wash.