Below is my solution to the resistor heat issue, FWIW. The fan at the bottom blows into the box and cools the Rutex drive inside and the air exits the top and flows past the resistor, which is bolted to the box along its rear edge. It stays cool enough to touch most of the time.
Final score on the servo drive. With the Gecko I could get a .015 cut at about 700 RPM max spindle speed. With the Rutex drive, I am getting an .080 cut at 1,100 RPM max spindle speed. There seems to be power available to exceed this, but the maching rigidity is now the limiting factor. Needless to say, I am well pleased with that result
I am sort of a servo junky now and I'm waiting on yet another servo drive, this time a Leadshine 810, to put the small NEMA 23 servo (from iteration 3 or 4 of the 4th axis project) on my X axis. Now I have discovered a small very reasonably priced ($180) AC servo drive made by the same outfit . . so probably I'll be playing with that sooner or later . . . my wife just got a new dining set, so I may be able to spend a little more on my toys . .
Review and comparison of the servo drives I have played with so far is here if anyone is interested:
http://www.thecubestudio.com/ServoDriveReview.htm