4.5.5 is partially stable. Random bridging/masquerading lockups on SMs. Power cycle or remote reboot fixes it but the only tattle is the throughput monitor, shows almost no data passing but the client can get to the SM and so can the support techs at the NOC, just not passing data.
Have been trying 4.5.6 on specificly bad SMs and so far those SMs are good. Planning a single AP upgrade to stress the firmware more than I can on the bench.