MXZ is shortest, 129 I think. Renegade is on the shorter end of crossovers, 137 I think. And Backcountry is a longer crossover, available in 146 or 154 I think. All available with the 900 ACE, 600R or 850 and have wide front ends and optional shock and gauge packages. MXZ and Renegade are coupled R-Motion skids I believe and Backcountry gets non-coupled T-motion I believe. .75", 1.6", 2.5" lugs depths available across those models iirc. Lots of speculation on my part as I didn't check the site just going off memory.
The backcountry 146-155 has a specific skid called the c motion, it's a xm t motion without the t motion knuckle. Also the backcountry has a little narrower ski stance then the mxz and renegade. That model is about halfway between a summit and a renegade. I have a buddy that mountain rides a backcountry and likes it.