When I did have the 5.1 board, I would test it outside the case with the cable stretched out and still encounter issues. It would detect the board, but would just hang on the "Reading disc". I truly believe my issue was related to a power supply, because every power supply I tested on it that didn't have a 3.3v rail it would boot fine and play with no issues. All my cabinets have a 3.3v rail, so it was pointless to keep the 5.1 rev.
I feel if you want it to just "work" without having any issues, the 5.0a+b rev boards are what you want
I feel if you want it to just "work" without having any issues, the 5.0a+b rev boards are what you want