Advice please: New springer, maybe an underlever

[CuppaT]

Evening All!
I have been considering a new springer and need some advice on underlevers.

I have been considering something with a long(ish) barrel as they are marginally more efficient, marginally quieter, and marginally less hold sensitive thanks to frontal mass. HW77 (standard) is then a good choice, but i can't see that they are sold in the UK (?)

HW77 = 470mm barrel - Are these sold / imported in to the UK? I fancy one with the laminate stock.
HW77K = 370mm barrel
HW97K = 300mm barrel
TX200 = 395mm barrel
TX200HC = 319mm barrel

What would be your considerations for an underlever, and do you have any tips that may swap my decision?

A spit polish of the internals of whatever i decide will most likely accompany a welsh willy kit (edit: or TBT kit)