Speaking personally, I suppose I'd probably go for the fine 1843 if it was no colon after reg. Undoubtedly scarcer than the REG: but judging by your figures, Ian, not "vastly the rarer of the two 1843 varieties", as exaggeratedly described by one dealer.
Oddly enough I had no difficulty getting a slender seven 1857, and have seen several for sale, but mostly lowish grade. The one I have is about EF, but the term "sometime cleaned, now retoning" could reasonably be applied to it.