I think I'll be happy with just the one HW55; although the set-trigger version is very appealing, its also very expensive! The tyrolean stock is ugly but very very comfortable, and the modest compression cylinder and relatively thin barrel make it surprisingly quick-handling- mine doesn't have the shroud. The muzzle sits on target OK without extra weight or so it seems to me.
Matt - I think all HW55 rifles are in .177, pretty much a dedicated target rifle. Although there is the one model which does NOT have the barrel lock, but shares the ordinary-type detent with the older HW50 (NOT the new one marketed as the HW99S), so it would be possible to make up a .22 version.
I remember the adverts for them in AGW in the 1970s, something about 'the pellet leaves the barrel before the reduced recoil is felt' which must have been hogwash even though the rifles were nearly as accurate as the recoilless rifles.
I am also fond of the HW35 Export, but I always feel the design is inefficient, such alot of cocking effort for the power it produces, with its oversquare bore and heavy piston. I've got three 'keeper' HWs now, a HW30S, a HW85 (old type) and now the HW55T. I think those are the best of the vintage wineracks! Although an old-type HW50S would be nice ....