I've been running 4 LABs off 2 Crown vz5000 in stereo and it seems to be a good match.
I've only popped drivers once, 1 box went down because a t-nut came loose on a driver and made an air leak. Other than that they seem to be able to handle as much as i can give them. I cross em at 35hz though as i'm a little weary of going any lower at high power and to be honest don't need to go any lower, there is plenty of sub.
On the RMX amps, i've been powering my Martin W8C's at 4 ohms off a 4050HD for a year or so i have spanked the arse out of them in all maner of dirty illegal rave venues as well as cold damp fields and beer covered night clubs, never had a problem with em. for the cash they are damn fine amps. My old mids ran 3x12's at 2.66 ohm off the 4050's and they loved it.
Going to have 6 LABs out in a pack outside this weekend all running of Crown 5k's, first time in the UK, much looking forward to the results.