I think it had a little lower vMax, 1.4v or so, but it could also lower it's clock frequency by Quad, rather than just 2x like the 7447a/b.
Tho there would likely not be any support for that in the Mac OS power management, as no 7448 ever shipped in a Mac.
Lowering the cpu clock, without lowing the voltage doesn't gain a lot anyway, my 7447's seem to run 5 C cooler when the power is set to reduced. There just is not support for voltage skewing in any G4 that I'm aware of, we can only find the resisters that set the vCore and lower it.