70-200mm Canon Mount - Trouble Deciding

Originally, I was deciding between the Canon 70-200mm f/4L ($635) and the Tamron 70-200mm f/2.8 ($769).

The Tamron is arguably as sharp as the renowned Canon 70-200mm f/2.8, at $500 less. I decided to give the Tamron a shot (I already have a Tamron 17-50mm f/2.8 that I love). The auto-focus can be (or appear to be) a little lazy in low light, but I really don't think it's as bad a people lead you on to believe. I did some quick tests and found that it is *not* front or back focusing, which were reported as problems with at least the early release copies.

Oddly enough, I think it performs well, but my confidence has been shaken by the fact that I have gotten "Error 01" half way through shooting in both times that I've mounted it on my camera. I haven't had any issues with others lenses. If I have time, I'm taking it back tomorrow to at least have it inspected, but likely to exchange it.

Now I'm heavily considering the highly coveted Canon 70-200mm f/2.8L, but $1300 is a big number to swallow given that I'm purely a hobbyist and there are times I don't touch my camera for a month. The Tamron has a 6 year warranty, vs. only 1 for this Canon. But both Canons have USM motors, while this one comes with a tripod mount (so does the Tamron) and is environmentally/weather sealed. The f/4L doesn't come with a tripod mount ($145 for official Canon mount), but it is a smaller and lighter package, which would be beneficial in some situations.

I'm mostly thinking out loud in front of a different audience. A friend says he wouldn't even second guess it - if he could get the Canon f/2.8L, he'd do it in a heartbeat. People on a photography forum had similar sentiments.

I have a Canon 480EX II flash, so I can certainly "get by" with the f/4L. I can think of a lot of things to spend the $600 difference on vs. the f/2.8L.

What would you do?
Re: 70-200mm Canon Mount - Trouble Deciding

FWIW, I picked up the 70-200mm f/2.8 just about a week ago. It is the non-IS version. The 70-200mm f/4L IS is sharper, but given my usage indoors, I opted for the f/2.8. One thing is for sure... it's a big and heavy piece of glass. Overall I'm pleased with it, but I have trouble finding $500 worth of benefits in it. I'm certainly keeping it (most likely), but the Tamron was just as sharp, and the AF was nearly as fast and similar accuracy based on my minimal test shots. In my practical usage, the Canon struggles in the same tough situations that the Tamron did. The Canon is smoother, and gives the perception of being faster (I think it's really mostly that it is quieter), and the USM motor is definitely nice. Manual focusing is much easier. What kills me the most is the 4.9 FOOT minimum focus distance (vs. something like 37 inches for the Tamron.) It makes it just that much more frustrating to use indoors, especially when I'm not used to such a limitation.