I think I first started having them in amps like Divided by 13s and Bogners in the early 2000's. The ones I have recently had are new and came in Bogner cabs for Goldfinger and the JB45 cabs.
Just tried the M65s with my Hiwatt and it's not bad actually. That amp is tight as all hell and quite bright, so the softness of the M65s kind of evens it out. Will need to really crank it though. This was at apartment-living volume. Loud enough to shake the floor, but not quite loud enough to get the amp/cab breathing.
I can see that combo being really good. My Hiwatt sounds killer with my Fane AXA12's which to my ears have a very Greenbackish mid forward voice. It also sounds fantastic with both my G12-65 55hz and 75hz.