I´m able to hit 4,9GHz @1,285V but not 5GHz @1,32V.
Is this normal? Do I have a bad motherboard?
Not the board. I'd go to 1.35v and see what happens. Not worth the heat for 1.4v only to gain another 100mhz. 4.9ghz at 1.285v is a good clock. I would suspect heat is the issue. What temps are you seeing under load?