They're both Marshall 2668 clones, so it won't make that big of a difference. It will just come down to the type of steel and internals. I'm thinking back 20 years, but I believe the OT for the Classic was different. I could be wrong. I do know the 101b is a 2668 clone. I had a Classic and...
I've had both the MM and the in-house. If you want the Mercury output tranformer, they're offering it now. It's their Marshall 2668 clone for the 101b.
I use the effects loop on my Dual for the Master Volume thing. It sounds a lot better to me. Mine has Philips 7581A power tubes and GE and RCA preamp tubes. I never liked the 440s. The 430s were a little thicker sounding which are the Sovtek 6L6WXT+ or EH 6L6GC (that's what they are today)...
Lastly, I remember some rumblings about Taylor swapping over to PCBs, so the newer ones are probably PCB. That wouldn't bother me one way or the other.