136" or 144"

http://www.youtube.com/watch?v=znDV5WTJS9w

I know your calling this your spring ride so if it was jumps, whips drops ect, i'd say do the 136 from experience. Just for the fun factor of being able to really throw it around. also the 136 would be far more durable on spring/summer snow for harsh landings and fly through the air a little better and level out better.

But since your talking about it being a loner/backup/girlfriend ride i would honestly go with a 146 and try to get your hands on a 2.5 camo extreme. That sled will go right where the best of em do because it has the added lug height but still a shorter track for better track speed. I almost got my hands on a 146 iqr conversion and it had the 2.5 track. So when you mentioned you may have to ride it when your main ride is down "which is almost always when it nukes out" id go for the longer track, 146 isn't even really that long anyways.

Hope that helps to see it from another perspective

also is the new sled a 600, 600 mod? 700 800?
http://www.youtube.com/watch?v=4a8v9ovkAZM

thats a vid of a 600 mod iqr in some deep dry MT pow. I can vouch from experience that snow makes everything trench even my old 163. But it still gets around pretty good.

if you ride mostly pow id go longer, there's a 146 for sale in the classifieds actually to...

I built mine into a 136/141 and love it, im into trails and off trail trees and whatever. Our snow only gets about waist deep sometimes deeper but I do just fine with mine.
What motor are you running?

I vote 144. you'll get better resale, better girlfriend track length, better used track selection, good back-up length to play with if your 155 is down.