I was looking at this Ebay auction, and saw that the motors are already fitted with the Dynamic DX connectors that I use:
http://cgi.ebay.com/4-POLE-INVACARE-M91 ... 2306f3c13f
I'm not crazy about the design of the chair it's from, a midwheel, but it's rated for 6.5 mph and a 400 pound user weight, and their sales data claims it will do 9% slopes and up to 3 inch high obstacles.
I find this interesting because the four-pole Invacare chairs are very common around here, and across several different models they all appear (visually) to use the same motor. Have they been selling a motor all along that is capable of far more than we thought?