the missing lens(es)

So I'm a happy K-7 user trying to resist deals on the k-30 body and k-5 body (thinking of waiting another gen might be best on that front).

I currently have the

18-55mm wr
50-200mm wr
35mm f2.0 fa favourite lens so far, colours seem something else (what are the other lenses with colour rendering like this?)
100mm wr

I'd like a wide lens (possibly fish), but funds aren't unlimited.

Things I've been contemplating

16-45mm
samyang 8mm fish
samsung or pentax 10-17mm
samyang 10mm if/when it comes out


Things that seem good but are steep ££

15mm
12-24mm


One idea was to get the 8mm fish and get something later to complement it.
With the 16-45mm would the f4 be a concern on the K-7? I've been using the 35mm f2 recently mainly...

The Samyang 8mm is one that is constantly on my list but never quite at the top when the money comes through...

It's also pricey but have you considered the DA12-24? (Always on my want list)