Bill,
To start with, I will indeed confirm that what you are saying is accurate. The reason I didn't bring up these important distinctions is because they have been discussed before, but it is true they have not been discussed recently. The mirrors are larger than those in the EMS scanner and on My DTs as well and there is no vignetting of my 5mm diameter beams over at least a 35 degree by 25 degree projection while the Y mirror on the EMS does vignette the same diameter beam over the same field. The cost of a complete 506 system with Steve's amps and two, good Mean Well power supplies is approximately 1/3 that of the EMS 8000 at $1,500. For what it is worth, I do not notice a thermal PROBLEM with the EMS scanners while projecting test patterns. My optical base plate is very well cooled and the tops of the aluminum mounts for the scanners grow only a little warm. I have not actually attached a thermistor to the motors themselves and the stainless steel case, although it looks nice does concern me a little here. The amps are another story and these do in fact require more than a good connection to an aluminum panel. The panel needs to be actively cooled as well.
Regarding speed, I can run the 506 to 34K over the above field with good performance on all the test patterns. Beyond this, the corners on the square grid which show little rounding at 34K begin to round proportional to the increase in speed. The DT 40s that I run over this same field with "5mm apertures" vignette badly with I would estimate about 1/3 total light loss. The maximum speed these will run with roughly the same distortions to the test patterns is 30K. The EMS 8000 can be run at 41K with the same quality in the patterns, but as I said above, they vignette.
Even without the mirrors we are working on these are very good scanners.