I am using a pair of old HS 55s to control a very small 100 mph TD 049 plane. The loads on the ailerons and elevator are not too great. The plane is supposed to be flown nice and smooth to record how fast it is. The control surfaces do not have very much throw and the linkage geometry gives the servos maximum leverage.
In a Mach None I would fly it more aggressively with a high roll rate and more carefree, dare devil way. I think a pair of HS 65s would be a good choice, especially if I put a lot of time into making the Mach None a "museum piece"