I'll throw in my two cents... I started off with a Rectoverb and really liked the Dual Rec sound. The ROV did not offer Tube Rectification, Channel Assignable loop, nor the option to run EL-34's, and there was a slight delay in switching channels.
I travel a lot and over the last year I found and played several older 2 channels of various revisions. It is my belief that the different revisions were Mesa's attempt to correct the cleans. I think revisions C-F have the best sounding Hi Gain of the Rectifier Lineage. Tight, Fat, Saturated. The Rev G with the right combination of tubes and OD and a slight adjustment to the Presence and Treble will sound very close to these older revisions. And guess what? The cleans are good too!.... But there is a price for those cleans.
Channel "Cloning". The manual states and "explains" how the red or orange channel can be configured to sound "exaclty" the same. "Want two red channels, " Mesa says. "How about 2 orange? Just configure the following..." Well IMO Channel Cloning never worked. My rev G has good cleans on orange, great modern hi gain sounds on the red, and great hi gain vintage tones on the orange channel. I was never able to get good cleans on the red channel. Thus the 3 channel models, which if you read the manual tell you exacly which channel (2 or 3) is voiced Vintage/Modern in the 3 channel models.
You wil note that Mesa does not mention channel cloning anymore.
That's my take on it. Mesa's quest for cleans in the rectifier ine. Which brings us to the Roadster and Roadking. Great cleans, great high gain sounds, and I think eventually good bye plain old Dual Rectifier.
