The Cobra is a softer compound than the Rip Saw, so keep that in mind when trying to compare mileage. Sounds like there may some marginal/ rougher conditions ridden by a few of you guys, but I have Cobra's on both my sleds (144's tho) and I really like them. If they don't last as long, I'll still take it because they work so much better. I mainly ride off-trail with some high speed trails, mostly in the UP, so I do my best to stay away from crappy conditions.
I'd say go for it, you'll like the performance, but you will give up just a little bit of side bite in the corners. Mine are not studded, and I can't forsee adding them either. I like it just the way it is.