AndrewJ, Very well written.
I looked into harmonic drive and direct drive when upgrading last year. In the end a Paramount ME was hard to beat. If I could have afford it, I would have brought this
http://www.astelco.com/products/ntm/ntm.htm - NMT-500 direct drive. But it was a BIG unknown.
Fact is, for astroimaging and 95% of the other work I do, a rock solid GEM with "wheels and worms" was the way to go. Also, the majority of high end images out there use a bisque or AP mount and support from Daniel Bisque wonderful.
cheers
Terry