An observation if you wish to get into serious macro like Yeatzee & Rense and start adding extension tubes/bellows/reversing rings etc - you need an aperture ring on your lens.
The legacy glass has that, as does the earlier DFA 100 macro, Tamron 90, the Sigma 105.
There are also the Vivitar 105 and a few other vintage macro lenses - though some have a problem with purple reflections onto the sensor (the early Tamron 90 had that).
On my Tammy 90 I use that aperture ring with my old Pentax K extension tubes. And my Tammy 90 is as sharp as any of them from what I've seen.
From what I can gather from images and reviews of the new DFA 100 WR (and I don't own one - so correct me if I'm wrong), there is no aperture ring. So when you want to go beyond 1:1 with accessories that don't transmit aperture info you have a problem
IMHO that's a limitation I won't live with.
The other thing to consider is that many people have expressed the opinion on this forum and elsewhere that
there are no bad macro lenses in production - and I would suggest that is the most useful statement to take home.
In the end it comes down to what you are going to shoot, what you are prepared to pay and how much you really want to stick to Pentax glass only.
Good luck with your deliberations!
Cheers