I know I'm allowed to go upto the next release latest revision,
So when I recieved my RB750 it had 4.11 so I put 5.5 on it.
It worked great until I rebooted, now it goes back to the old splash screen and shows version 3.11

I now notice that the RB750 is an os3 device... does that mean I'm only eligable for V4.x ?

Nevermind I think that was some sort of splash page since my proxy server was enabled. Once I disabled the proxy everything worked as normal...

This is my very first routerOS device so I'm stumbling thru it.