My main lens is the SMC Takumar 50mm f1.4 and my wife's main lens is
the Pentacon and I can definitely say the Pentax is a lot worse wide
open; in fact it resembles a Helios wide open i.e. hilarious. Oddly the
Helios at around f11 becomes really really sharp in the centre and
overtakes the Pentacon although the edges really never seem to catch
up.

However I think you can see the general direction of all the posts...
:^D