Darin, that's a lovely shot of the kids.

I agree that for a static subject or when using manual focus the Tamron is OK, however, you have the benefit of the A900 viewfinder. Try Manual Focus with the A230 in those conditions, not a hope in hell. I suppose, by trial and error, he may get enough keepers from a session or he could focus on a static object and stop down to increase the DOF but that defeats the object of a fast lens.

I don't think you read the OP's post thoroughly; apart from the stage shots he wants to shoot "(candid, fast action, sports) " and that's not the forte of the Tamron. Look, I'm not saying the Tamron is a bad lens in all circumstances, just that the OPs intended uses for it make it so; also, with a budget of $1200 + say $400 for the 80-250 he's not far off the price of a top notch lens that will cut the mustard in both his reqs.

Don't know about the Sigma equivelent but I do know about their QC.