I'm not overly concerned with weight, but my frame's a bit on the chubby side, so would prefer to try and keep it down where I can, without diminishing returns. Think the Zee would add 140ish gram over the Xts iirc.
I've personally only ever had great experience with Shimano, so would prefer to stick with them - certainly won't be thinking of going Sram Guide or the like.
Frankenbrakes rule!
Pretty good thread on the subject here: http://ridemonkey.bikemag.com/threads/frankenbrakes-and-brake-improvement-discussion.274164/
New XT 4pots seem good. Not sure on weights etc. Not that I normally look at weights.......as I'm not some xc weight weenie

Hoping mine need a bleed. But I loved the zees, but prefer the XT levers. Plus Ispec II. Nice link! Looks like it should work easy enough.

