I just had a briefing by Boeing and the cabin will be 6000'.
The reason for the 6000' was that they can lower it from 8000 since the carbon-reinforced plastic can withstand the differential pressure, a metal cabin would have to be a lot heavier than the current cabins to get the strength required to sustain the pressure. The reason that an electrical press and a/c system is better is that with electrical systems you can match the demand and requirements much more closely. A pneumatic system is less efficient and a lot heavier and more complicated!
The fusleage barrel that they just rolled out in a single piece (7m x 5m or something like that) would have had 1200 pieces in a metal fuselage barrel and would have been held together by 40,000 rivets...so there are lots of reasons for the move to the carbon reinforced plastic (or is it plastic reinforced carbon ;-) )