you really have to define "lugging" better.
yes there is a minimum rpm to keep the oil distributed, but I don't know that it is 1800rpm, or even 1000 rpm.
http://ecomodder.com/forum/showthrea...tion-4536.html
http://ecomodder.com/forum/showthrea...nomy-3159.html
Key concepts:
1. the rpm must be sufficient to keep the oil layer intact, i.e. above idle.
2. Bearing wear is a function of rpm and load at the low end. extremely low rpm is usually pretty low torque for an ice, so it is somewhat self-regulating.
3. if you are centering your shifts on bsfc peak, you don't really have anything to worry about anyway.
I just don't want folks racing their engines out of an irrational fear of a $3500 engine repair bill.