We use a MS250 stack with MS250 access switches.
The stack is connected to a pair of ASR routers and a HA pair of MX's.
It was a long time ago, but we had some strange issues when on a occasion switches rebooted cause of a power failure. The stack remained up due to a connected UPS but the clients could not get connectivity once the access switches finished booting,
Can't give the details anymore but i remember support pointing out to this issue.
So we've stayed at 10.45.