I think it may take longer that you're expecting to get from 70-80. At least a couple weeks unless you're playing well over 8 hours a day. Since you got burned out before then I wouldn't suggest trying to power through the leveling that quickly. If you're sure you want to MB then I would suggest start working on the team using RAF and using up your DKs rest exp when available. You could get the rest of your team up to 70 much more quickly than getting your DK from 70-80. Plus, if your whole team is 70 together then leveling from 70-80 won't take nearly as long as DK from 70-80 followed by rest of team from 0-80.

Confusing enough?