Hi all!
Here's another vote for the DA* 16-50...
I just picked mine up this past weekend and got a chance to put it through it's paces this week on a trip to North Carolina.
Weather-sealing is what drew me in, but the sharpness and SDM are what have really impressed me since I've had it. You don't hear it, it just focuses!
The only down-side, IMO is the size. It's a big lens, especially compared to the DA18-55.
Instead of buying the lens before your trip, why don't you get it when you get here? I always hear about how much cheaper Pentax equipment is in the US, compared to Europe...
Here's one of my favorite shots from my trip. I took this week with my new DA*. It's a swarm of bees that was temporarily hanging out (literally) in a tree. The shot was sharpened and just a bit of fill light added in ACR. 50mm, f/5.6, 1/60th + on board flash for fill:
and a 100% 800x600 crop from the same:
I had been tempted by the 16-45, but couldn't justify "replacing" my DA18-55 with an even slower lens, at least at the wide end. I'm planning on keeping my DA18-55, just because of it's size, and will use it when that's important.
Good luck deciding and have a great trip!
-Chris