I have a 03 SKS 700 144" track and 1.25" lugs.
These sleds were the inspiration to the Switchback. great all around fun sled,Good powder rider and good trail rider.
RMK is all business for mountain riding with a much taller lug, Great climber and deep powder performer but may not be as as good in the trail. The deep lugs tend to propell the sled straight regardless of the direction the skis are pointed in.
i have a rmk and a switchback (sks) the switch is very good on trails but not at good as a trail sled but it is also very good in powder (floatation) but not quite as good as my rmk. Basically the crossover is a rmk, with smalle lug track so cooling the engine and slides on trails isnt an issue, and it has a better shock package. The gearing is a little different as well. My rmk will climb anything and no snow is too deep, but it was rather crappy on the trails.
Older RMKs were also set up with different needles and slide cutouts in the carbs, more for higher elevations. The Switchback is a bit wider than an RMK, due to wider ski stance. The seat is different, as well. Other than the things already mentioned, not much else is different. If you have a 144" RMK, it's very close to a Switchback.