Thanks for that my legs are long for my height, I have mine about 1.5 cm lower, as I pedal 'heel down'. I think your right on the TT length, my current Niner is 25.25, so the TallboyXL is nearer at 25 inches (I have a 100mm stem).
I could probably ride both, the jump to a 26inch TT may be too much. Head tube length is another consideration, the TB ones look short. I also have wide bars at the mo , so increasing reach….too much thinking, I'll just give it a go
Looking forward to the test ride and to racing when I inevitably cave in and buy one!!