Don't sell any older wides till you tried them on the K1.
I do think the 24/2.8 (presuming that its the same the K24/2.8) will work well enough.
I've tried a friend's copy of the FA20-35 before and though his was decentered on one side, the other side was really very good.
I have doubt about the A20/2.8 from the one I've tried, though others have reported good results.
I'd just get a Samyang 14/2.8 (or Irix now) and the K1 and be done with it.
---------- Post added 11-21-2016 at 07:06 AM ----------
Samples of the lenses on the K1.
K24/2.8 - not as sharp on the edges, but really good enough if its adjusted to reach infinity (or a bit past it ).
---------- Post added 11-21-2016 at 07:11 AM ----------
Samyang 14/2.8 - despite what is said about distortion, I find that the LR profile cleans it up enough to be not much of an issue.
A steal at its price.
This lens is sharper on the edges and corners than many of the legacy wides I've tried (and its 14mm not 15mm, 18mm, 20mm, 24mm).