Consider that 150 RPM is the slowest speed.
Large diameters or threading may be difficult at that speed. Also, is there power crossfeed?
does it matter to you? How big is the drive belt? the 9x20's had a puny belt - 5 mm wide I think. It would be good to see what you are condisering buying in person. Maybe Grizzly can tell you of someone nearby who has the same machine.