GlueBall-
I guess you've been fortunate to have flown a/c with that kind of performance. We have several models in our fleet that any warmer than ISA +10, our altitudes would be around 14-15,000. Here in the US, that's a problem west of Denver.
ITCZ-
We plan both Terrain Avoidance (on filed route) and Driftdown (with escape routes). Many times we'll be too heavy to dispatch TA, so we have to dispatch DD. The US regs say no person may "take off" an airplane at such a weight, etc. Now, if you're in flight, that FAR was satisfied at takeoff. The PIC is now free to fly any route he chooses. He may choose to avoid a line of thunderstorms, or pick one with smoother air, etc. That wouldn't be reckless. Also, you may find that flight conditions (ISA, fuel burn, winds, etc.) may be different than planned. In those cases, minimum rate may be what you're looking for.