Not sure about the vanilla G400, but I think its something like 125/150 core/mem speed, using a 300 MHz RAMDAC.
The G400 MAX has a core/clock of 166/200, giving it a healthy performance boost over the vanilla G400, as well as a 360 MHz RAMDAC.
The G450 is using 166 MHz core speed and 166 MHz DDR SDRAM, which is pretty much the same as 333 MHz SDRAM, but its memory bus is reduced to 64 bits, vs the 128 bits of the G400's, making bandwidth somewhat higher than the G400 vanilla, and somewhat lower than the G400 MAX, the RAMDAC is at 360 MHz like the MAX.
Since Matrox are sorta secretive about this info, some of it might be a little off, feel free to correct me.