For longer diversions (more than 45 minutes), I normally flight plan FL220 for most flights, otherwise FL150.
Type, L1011.
Sometimes you get higher from ATC, sometimes not.
However, I have seen plogs wherein FL310 (or even higher) is planned, and this is truly unrealistic for all but the most unusual situations.
I do not like steaming around with absolute minimum fuel (or even less) in tanks.