Recently, I sold my Tamron 90mm f2.5 Macro (52BB) to my friend and got this Tokina AT-X 90MM f2.5 macro.
My impression is this lens is also suffered from Tokina's bad characters, pal in color and low in contrast. For me, it is really hard to say whelther Tamron or Tokina is better for Pentax; although I think that Tokina is a little bit sharper but sharper is not everything.
I think both lens are good but comparison of pics results would be decided by the man behind, not by the lens itself.
The weather for taking these shots was windy, cloudy and cold. My hand was a little freezing and shaking, so may be it was really too early for me to put the above comments.
Thanks for watching.