Quickly taken, handheld examples of the Tamron 18-250 at 250mm below. Excellent lens - haven't seen/tested the Pentax, but after shooting outdoors with the Tamron for a couple days, it's hard to see how the Pentax version could perform any better.
The Tamron coating is about the same as SMC, also, as far as I can determine.
Both of these are uncropped, and I think the first is slightly sharped in picasa, the second is untouched.
1/350s f/6.7 ISO 200 250mm
If you could zoom in to his eyes, you'd actually see my reflection and make out the circle of the lens pointing at him. Amazing sharpness/resolution at 250mm. Rivals some of my primes.
1/250s f/6.3 ISO 800 250mm