Good luck with your hunt Sten! Macro lenses are often the sharpest lenses in any manufacturers lineups and as such, its really rare to find a 'bad' macro lens. Pretty much any macro lens you get will have comparable image quality to any other macro lens. As such, your search for the perfect macro lens for you will come down to other lens features, focal length, and price.
If you want to stick with a macro lens that can double as a portrait lens, Id certainly look at macro options between 70mm and 105mm. You can also look at the 50mm macros, but those shorter than 50mm and longer than say 105mm, wont fit your portrait option very well. If you already own a "Fast Fifty" lens, you may want to avoid a macro in that same general focal length, as youve already got a solid portrait option. This was the situation I was in when I bought my macro lens...I had an FA 50 1.4, so getting a 50mm macro seemed a little redundant. I chose the 100mm WR instead. Another thing to consider is the working distance between the subject and the lens. Naturally, youll have to get closer to the subject in question with a 50mm lens vs a 100mm lens. Depending on your intended subject, this can be complicating. Flowers dont mind it much if you get super close to photograph their beauty, however, the local wildlife might, and if you intend to shoot closeups of a live untamed subject, a longer working distance will likely increase your chances of capturing the moment.
I suspect the price/cosmetic features will play a more integral role in your choice. At well over $800 now, the 100mm WR is a bit of a pricy option for a macro lens, especially when you can get a Tamron 90mm for about half of the cost of the Pentax option, and the Tamron lens even has a focus limiter. The tradeoff however, is that the Pentax lens is weather resistant, offers quick shift focus, and has a metal constructed exterior that has a much more 'Limited' feel to it. Additionally, the size and weight of the Pentax are very compact and light considering how well its constructed. Is it worth the extra cost in features that wont really impact the image quality? Thats up to you. Thankfully I dont have to agonize over that decision again!