I know Air Mauritius has bunks installed in the aft section of their -200ER's. Unfortunately do not know too much about how comfortable they are,etc. Just for your information,my company operates a -300ER and we do JNB-LGW which is just shy of 5000nm. We have a two class configuration(230 pax total).We are field length/Alt limited out of JNB which is 5558ft amsl on a hot summer evening and are unrestricted out of LGW. The flight time is on average 11:30.Hope this sheds some light.