Do remember fellas that the D'lite has evolved significantly in the past year or so.  It's to the point where you have to ask.....Which D'lite?

I would definitely say OT has more mids than the SF Twin I played and not vice versa.

With the OT which is very strong in the mids like Wyatt said, you don't need to do that. So if you are looking for strong firm mids, OT is definitely for you.
Bass and treble are already there.

Much of Texas Flood used a Dumble, but I can't comment on which songs (I'm no SRV fan).

Link.....?

You are really comparing different amps.  So, you need to decide what it is you are going for.  If you like Dumble tone, then they are probably the best pick, and the most versatile at covering clean jazz and modern, overdriven blues and classic rock.  The high-gain preamp is great for slide work. 

The Overtone Special is Dumble based (40 watts, BTW).  The Dumble design isn't about power tube distortion.  The idea behind the Dumble (like most preamp OD-based amps) is a high-gain preamp distortion into a clean power amp that keeps the sound tight and defined.  That's why these sound so sweet when used for clean, hey are optimized for a clean poweramp.  Most Dumbles were build around the clean Fender 85-watt Twin Reverb poweramp, and modern amps that use the high-gain preamp idea all keep using bigger and cleaner power amps.   Yes, you can crank the power amp, and being Fender based, you know it should sound nice and musical, just know the amp isn't designed around that idea.

The JTM-45/BB on the other hand is all about cranking.  The preamp is low-gain, the way to get OD is to crank the amp and get both the preamp and poweramp cooking.  Less saturated and less defined than the Dumble, it's going to have a bigger,  "browner," fatter power amp crunch.  Marshall!  Though, it's going to be bluesier, with less gain and more sag than it's tighter, hotter rock'n'roll cousin, the 50-watt Model 1987.

Now, the Expression, on the other hand, is based on an amp design for rock.  The goal Marshall pushed to the limited, but with more clarity and note definition.  It's all about a hot preamp with a power amp optimized for crunch. Personally, i think they sound too buzzy, maybe Fischer tried to get too much gain out of too few preamp tubes?

my own tastes?  The Dumble for jazz, hands down.  But I'll take a 1987 for rock (my tastes lean more to '70's/'80's hard rock).  For blues, I'm a Tweed Fender kind of guy (not a modern "guitar blues" fan, I like the early stuff), but I'm sure I could dial in fine tones on the Dumbkle too.

Does this qualify as "clean"??

That is the concensus with these amps but don't forget the Overtone has a lot of flexibility and can cover a lot ground tonewise with a bunch of different speakers.  The only speaker that I didn't really like was a V30 I tried for interest sake a while back.  But Greenbacks, Emi Wizard, RW&B, Tonespotter, and Sammi's all sound great.