I am likely to upgrade anyway. I did upgrade the firmware to v4.1. When I bought it, it was v3.0 (I think), and agree that it was much like Sigma then. Now it's more consistent and acceptable (still, could be better) and I'll stick to it.
BTW, you can't update the firmware in a Sigma.
I also upgraded the firmware in the K-5 to v1.14 (don't remember from which version), but didn't notice any difference.
I didn't mean to ask about the AF but since Allison mentioned it I'll ask, is there noticeable improvement?
I never had much problem with the AF in low light conditions. In good light it even worked fine with 10-stop ND filter on.
Occasionally however it was back focusing when doing portraits with low depth of field (f/2.8). Although it showed it locked focus on the face, it actually focused on the wall 5 feet behind which was very annoying.
Thanks for your help.