There is still a problem with RouterOS 6.xx and Nstreme+Polling radio disconnections. Comparing to ROS 5.2x it's not working good. At the ROS 6.xx there is much more disconnections CPE from AP - both at the same 6.33.3 version (checked at every previos 6.xx version - the same).
MikroTik team - cold You repair thet annoying problem with ROS 6.xx version. At this point we don't upgrade to 6.xx due to radio problems with it.