Matthew, thank you for your comment and congrats on your new Pentax.
Without having experience with the Tokina lenses, I think that you would not regret the purchase of the Pentax 16-45 mm. It gives indeed very good results and I am very happy with it. Almost ruined after all my recent lens purchases, but happy ;-).
Regards and enjoy your new lens. Looking forward to your macros.
Gaby.
BTW, I managed to get a Pentax SMC-F 100/f2.8, how I love macro :D
And looking at your shots I am also tempted to swap my Tokinas for a Pentax 16-45...