I'm not sure about the two stroke trannies. But the four strokes,..the MXC and the SX share the same tranny, whereas the EXC tranny is completly different; 1st, 2nd, and 3rd are much lower on the EXC, 4th is the same, and 5th and 6th are much higher on the EXC.
I have an 02' SX400 with 12/54 sprockets, the 54t rear will fit the stock guard with the wheel pulled back a bit, (longer chain). I got nearly a whole season out of the slider with this sprocket combo. The slider is only $16. small price to pay to have the correct gearing for your needs.