> ...and a non-tired engine will use no more oil at 3500 than at 1800.

I'm not disputing that because I believe in almost every application you are
correct, but I did find this article interesting. It explains how low load
operation at 4000 rpm causes oil consumption problems in the '97-'01 LS1 and
LS6 Corvettes.
http://www.idavette.net/hib/02ls6/page5.htm