Because of the compactness of the large shaft diameter (theoretically the diameter of the 6" disc of the DM-6) and the close coupling of the telescope to the mount, the mount should be extremely rigid. To find out how rigid I performed the following test on the DiscMounts' DM-6 head.
For the test I used an old black Celestron C-14 tripod (over kill). Since my Tele Vue NP-101, 4" dia., 26" long telescope has a single ring mount securing the telescope to the dovetail plate, I added blocks between the dovetail plate and the telescope tube in front of and behind the ring mount. This should eliminate most external problems and give a good idea of the rigidity of the DM-6 head. The eyepieces used were a Tele Vue Nagler 31mm type 5 for low power (17.4x) and for high power a Tele Vue 3mm-6mm Nagler zoom mounted on a 2x Powermate (360x).
The results are as follows: At 360 power the tapping on the rear of the diagonal there was near zero vibration. If I pushed hard enough (just below the force required to move the telescope), the image moved and returned with no vibrations. I also had no noticeable effect from a constant 10 mph wind with gusts to 20 mph. In addition, holding on to the focuser did not make the image jump around.
What good is rigidity if the mount is not smooth? My DiscMounts' DM-6 mount is adjustable to handle a 2.2 lb. eyepiece with out rebalancing (or changing the friction adjustment) when changing to higher powers. It is still very easy to track Jupiter as it glides across the eyepiece at 360 power (360x is obviously much for a 4" telescope, but this was a mount test not a telescope test).
Longer telescopes will act a little different. From my experiences, they are easier to move (smoother) and they are surprisingly rigid.