The maximum extension I'd probably ever need is around 30cm so I think even with fixed plate on the TK would be ok for me. I may have to rule it out anyway though as there's still that annoying quirk with my 90mm XL where the rear cell is too big my a few mm to fit through a Technika/TK board without unscrewing the protecting ring on the rear cell of the lens. Overall the XL lenses are easier to use on cameras like Sinar, Toyo monorails and Arcas that have larger front standards. Although the TK still seems like a wonderful camera.
The thing about Sinars - I'm not finding there is as much used stuff available as people tell me - at least not anything in fine condition. So far I've found very few used Sinar opportunities actually (although still more than Arca).