I supose you can get away with running wide open throttle in a high gear/low engine speeds on some cars...
I run 90% (not 100%) for exactly the reasons you stated. With fuel injection the computer thinks you want max power if you give 100% throttle and goes into open loop control (ignores the oxygen sensor) and dumps in lots of fuel. That is bad.
Your comment about deisel engines being regulated by fuel delivery and not a throttle plate... that is one of the reasons they get better mpg than gas engines at partial throttle. No pumping losses across a throttle pate.
the problem of pumping loss as I understand it:
A partially open throttle reduces the manifold pressure, which reduces the pressure on top of the piston as it is travelling downward, sucking in air/fuel. Since the pressure on top of the piston is much less than the crankcase pressure, the pressure force is working against the piston (slowing the engine). At 90% throttle opening the manifold pressure is higher and it isn't as bad.
Just some thoughts and I am happy that there is a forum like this to further ones education. I love to learn about this stuff!