I cannot comment on the 12" Lex Paragon, but can provide you some feedback on the 10" f6.3 version.

It is an OK lens, which I use on 4x5 and 5x7 mainly for portraits and some landscape work as well as closeup work on 8X10 (only closeup as it does not cover the format at infinity). It is a little soft at the edges through f16 and then evens out at f22.

I imagine the design of the 10" and 12" are similar so I would imagine you would see similar results.

- Mike