Anybody have any input on the effect of the reduced speed? Am I correct in my thinking that it should only affect the time it takes?
Until I stand corrected, slower speeds (i.e. 85 RPM) generally shouldn't impact your grist. From the material I've read, your grist and efficiency are most impacted when roller speeds exceed 300 RPM, but I'm sure that's mill specific (3 roller mills may be affected less than 2 roller mills, etc.). I can't really speak to whether 1/6 HP will be enough. I upgraded from the 1/12 of the Surplus Center to a Leeson 1/2HP.
Here's some additional info about RPMs for the MM's. Per the Monster FAQs:
"What RPMs should I run my mill at?
The best speed to run all of the drill driven mills at is around 150-250 rpms. Does it have to be exactly 200 rpms? NO WAY. A range of 100-300 is fine, and if you are willing to have a little more flour, then you can run it a little faster. I generally tell folks to run it as slowly as your drill will run it without stalling plus a little more. It usually takes a little more torque to get the mill going than to keep it going, so you will have to give it some more power to start the mill, and then slow it down once you are milling. You should experiment with faster/slower speeds and see what it does to your grain."
It might be worth asking Monster about though -- in my experience, he's been easy to get a hold of and very helpful.