[Alfie1965]

I'm just getting into this too and haven't gotten a good look at enough decent glass. Got sample pics?

I had an FA 80-320 lens, and now got the Sigma 70 -300 APO. Comparing the two I would say the Sigma has the advantage, but only slightly.
If you are using a DSLR I would opt for the Sigma, but with Film I would go for the Pentax.
Size wise they are about equal when fully open, the sigma is shorter when retracted and also comes with its own carry case as do all sigma lenses.
As for lens quality, both are good quality budget lenses, with softening of the picture at full magnification.
I have posted a picture of my daughter (devil in Disguise) taken with a Film MZ10 and the 80-320 lens at 200mm, remember this has been scanned also but you can see the quality and depth of colour and one taken with the same lens on my istDL2 (splash) this one is at 300mm but has been cropped so doesn't show the whole picture. I don't think I have posted one taken on the Sigma yet but keep an eye open I will.
Hope this is of some help.

[SpecialK]

the tamron was sold out all around toronto.... i guess more people around here are buying that tamron lens... i guess it says something about the lens.

Or Canadians :-)