"They aren't designed to turn 20 rpm's. I would think it would destroy the bearings and gears in short order. "

apparently you've never seen a house with electric heat, electric oven & stove, many indoor and outdoor lights and a dual element electric water heater all on at the same time. [Linked Image] i think it turns like 60-100 RPM [Linked Image]

i don't think 20 RPM will burn it out, but you probly only need like 5 rpm or so in order to look good. my meter lamp only goes like 1 RPM or less with the 150 watt bulb.