warming up a motor with no load on it is bad.... its during this time that condensation builds up inside and will literally wash the walls of the cylinders from oil.
not sure how much condensation do you have in your oil for it to wash your cylinder. IMO, if there is a condensation on cyl. walls, it is better to burn it off with lower rpms.
Also, condensation commonly develops when things cool down, not when they warm up.
Anyway, IMO there are two elements to the warmup process, one having to do with how the engine runs, and one concerning clearances/thermal expansion of metallic parts, lubrication, and wear. Aluminum pistons Must
be at close or at the operation temp to work as designed, even hypereutectic ones.
I run forged piston in my thumper and warm up is a must there. Piston slap can F-up the cylinder in no time.
I agree that idling for a long time is bad for the engine and fist of all for the environment, however simple 5 min warm up is pretty important IMO.
The only engines I do not warm up are my diesels. They are so darn efficient, they never warm up without any load.