Hi, I'm Brent - the engineer that Stephen's referring to... Stephen and I had extensive email correspondence during the time I was putting the TC-15 through it's paces. I'll try to compile all that and post it here, but in the meantime, thought I'd chime in on the question of speaker choice...
Now, I don't have a cab with either a Blue or a Gold (will soon though!) so I can't speak to those particular speakers, but I did run the TC-15 through a number of cabs with different speakers - the results were interesting, and somewhat surprising to me!
But first things first, these are the cabs I have in my studio
Orange PPC212 2x12 Cabinet (V30)
70's Hiwatt SE4123 4x12 Cabinet (Original Fanes)
Mesa Boogie "Oversize" Recto 4x12 Cabinet (V30)
Marshall 1960A 4X12 Cabinet (G12T-75)
Marshall 1960AX 4x12 Cabinet (G12M-25 "Greenbacks")
Marshall 1965A 4X10 Cabinet (G10)
60's Fender 2X12 Cabinet (Original Oxfords)
Peavey 1x12 Cabinet (G12 "Classic Lead")
Now, FWIW and for sake of comparison I also have an AC-30 (with Greenbacks). I LOVE this amp and it sounds GREAT with Greens (and obviously Blues too!!). I should also mention my favourite cab is my Hiwatt cab - those Fanes sound amazing with everything... well, almost everything...

And for context, my testing was done during recording a young band I'm working with. The music is rock with everything from clean/slightly dirty tones right through to ripping high gain!
OK, so what did I anticipate would sound best? I thought for sure my Hiwatt would kill with the TC-15. I thought I would love the Greenbacks because they sound FANTASTIC in my AC-30, and with every other amp I own with a "vintage" voice. And I would expect my old Bassman 2x12 to sound amazing too (admittedly I haven't tried this cab with the Trinity yet - tomorrow!!). I expected I would hate the V30's and the Marshall G12T's...
OK, so what actually sounded the best?!? Drumroll please... for my tastes, the V30's!!! Both the Mesa cab and the Orange cab are PHENOMENAL with the TC-15. My favourite sounds of the bunch. I also loved my stock Marshall 1960 cab with the G12T's - I was very surprised by this - I usually only like this cab with my high gain amps. And the sleeper KILLER cab was the Marshall 4x10 - Wow! This was a special combination. I think the way I put it to Stephen was the TC-15 with the Marshall 4x10 was like the coolest combo amp I've ever heard!!!

My least favourite cabs? The Hiwatt and the Marshall with Greenbacks...
OK, so why was I so surprised and what did I expect? Well, the TC-15 is a very bright amp... VERY bright! As Mattia has suggested, I expected I would want a speaker to tame the top end somewhat. But what I learned in my experimentation is that the majority of the very special character that the TC-15 possesses is in it's top end - taming that with a "warmer" speaker kind of killed the character of the amp for me - made the TC-15 sound somewhat blah and generic (which it is ABSOLUTELY NOT!). I found that the brighter speaker choices really enhanced what's special about the amp and brought out it's true character. Having said that, I did have to use the "cut" knob more to it's extremes, but the result was the top end was smooth and all the true character of the amp remained...
So my first post was a long one!! I'm going to get out of here before you folks get sick of me already! Hope someone finds this useful.

_________________
Brent Bodrug
Producer-Engineer/Songwriter
www.slyfichapel.com