So, while digging through various forum archives to find as much info on the MXR as I could, I found this tidbit over at VitalMX.com:
When you look at the specs for the MX vs MXR, note the final drive is 12/53 on both, but the gear ratio is 3.5:1 on the MX, 3.53:1 on the MXR... they've played...