George wrote:

"Now, please excuse me if I break the wind on this fuels discussion,
but how in the world are you going to keep auto gas from vapor locking
going from 12,000 to FL 250 on an August day?  It is not easy to that,
now, even with 100LL."

Excellent point, and my answer is "beats me."  I know of several stories
of airplanes heat soaking in Phoenix at 125F ramp temperatures, and
after the avionics finally cooled and started to work, the climb to
altitude and cruise were entertaining until the fuel cooled down.  And
this was with 100 LL.