Sounds like you've really done your research. I'm not sure if there's much I can add. When I was in your position, I took a chance on Tamron and came out OK. Others have not been so lucky, but that's what I would still recommend to you. Think of it this way: with the Tamron you have a chance of getting a bad lens and the hassle/expense of returning it. But with Canon you are 100% guaranteed to spend twice as much money. I'd rather take the chance.