You can cross the K2 Cinch off your list. Don't bother with them. BOTH the guys I ride with had them last season and they BOTH broke. One had had his a couple of seasons, the other's broke on his 2nd day using them. Luckily he brought his old traditional bindings as a back-up.
On one, the cable clamp snapped just from the pressure of locking it. On the other, the heel loop snapped.
Not to mention the chrome paint rubbing off them on the first day.
The problems with K2's rear-entry bindings are:
1.) They have too many moving plastic components.
2.) K2 only has a couple of rear-entry bindings. The don't specialize in them like Flow and Gnu, which for years have only been developing rear-entries.
3.) Cheap materials and construction.
For reviews on Gnu bindings, I saw a few last season on dogfunk.com, which you can still view. Here's a really detailed review of one of this season's high end Gnu bindings.
The guy covers a lot of important stuff that you would consider before buying bindings, and after reading it I wouldn't go with Gnu. There's also a Gnu binding review on Angry Snowboarder, which said they were ok but nothing special from what I remember.
The only ones I would consider would be Flow, but only one of their high-end bindings.
Their low-end bindings are made with cheaper materials (all plastic) and I've know a guy who's Flow baseplate broke a couple of seasons ago.
The high-end ones look pretty solid though, and they have ratchets on both of the straps if you ever need them.
Just read reviews of this season's
Flow bindings. They've made numerous improvements in construction and performance, including having 2 separate straps.
Just make sure your boobs will fit ok with them. Sometimes that's the only problem. You can try all this out if you order from Dogfunk, which has a great return policy. If you get them there and decide you don't want them, be nice about it in the chat box and they'll give you the return label for free (free exchanges are already supposed to be free, they told me). They always have given me free return shipping, and I 've tried out and returned a lot
of stuff from them!