I've always thought that running an engine under no load at high RPM is alot worse. What are you guys' thoughts? This is for an engine which makes all its power under high RPMs.
I think of it as trying to hit a punching bag (load), and missing the bag (no load). To take the comparison further I've thought of idle as just shadow boxing, where no power is really being put out.

 

I have a friend who had some fast cars back in the 60's. He said he would always break in his vette's on a long straight road, running them up to redline in 3rd and 4th gear, then coasting back down while still in gear.

Of course, the materials everything was made out of were probably different from today, but he still said he would never rev the motor without a load

 

Here's an interesting thread about this:

http://ls1tech.com/forums/showthread.php?t=556816