Another common focal length in my collection (and others' as well) is around 50mm. I have five ways to play right now: Rikenon XR and SMC-M f/2 primes, the DA50-200 (max f/4), a Quantaray 28-90 macro (f/4.5 at 50) and the DA40 Limited is close enough. Oh rats I forgot the 16-45 at f/4 - so a supplement will follow soon!
Tests were not precise: hand-held and manual focus at the widest apertures, since they will all be fine at f/5.6 anyway. All were shot with auto ISO and WB, and as DNG raw files with the K-01; no processing other than posting from Picasa so its raw defaults are shown here.
Depth of field was an issue with the f/2 primes, as the center of the bud and the pollen stems are not a match with the petals. Anyway, in this case the no-surprise winner was the DA40 Limited, which loses a stop to the f/2s but is a modern optical marvel and a mechanical throwback with its all-metal construction. Second* would go to the 28-90 macro; this lens dares to perform well despite its bargain-bin price of $35-50 most of the time. If you hit the first Ritz closeout it was under $10, which is what I paid to go with my Sony Alpha A200!
The two 50mm primes did pretty well but contrast was down a bit, likely from their older coatings. The 50-200 has a fairly long minimum focus that is better suited for flower shots above 100mm. Still, the image is decently sharp with great color & contrast.
I've tried the DA40 with a bargain +1 and +2 closeup filter attachment, and while this brings one closer the images are just not the same. Sure your DoF is razor thin, but it just looks less saturated and less amazing. No doubt a $100 closeup filter would outperform a $10 one, but we use what we have not what we might consider. The DA40 Limited does excellent work and can get pretty close, and for me that'll do.
* Update: the DA16-45 is quite good also; exposure was a little brighter but the time of day was different. Sharpness and bokeh are pretty similar on this shot. And I got a bee-fly in the scene (lower right), that's pretty cool!
DA40 at f/4 at the top.