Like the title says. I've recently purchased a Tamron 17-50 f/2.8 to couple with my 40D and so far love it. I love the speed and constant f/2.8 throughout but I'm worried that being limited to 50mm on a one and a half month backpacking trip around Europe will be to short. I've decided I'm only bringing two lenses (since everything must fit into a 55L backpack I can't afford space for long telephotos), one of which will be either be a Tokina 12-24 or Canon 10-22... but that's another post.

Basically I want to know if it would be worth selling my Tamron to acquire the longer length of the Sigma. I know the Tamron is popular for it's speed and sharpness, but I've read some decent reviews on the Sigma as well... What do you guys think?

You are not alone.

I have been toying with this for ages, I currently own both the Tamron AND the Sigma 17-70 and it hasn't helped. They are both very good lenses, but the image quality is definitely better from the Tamron.

I ended up buying a 70-300 IS to go with my 17-50 on holidays as I value the constant 2.8 more at the shorter lengths and then I'm only missing 50-70mm from 17mm to 300mm

The Sigma is surprisingly good though, better than I had expected, but it is quite slow.

There just isn't a one (fastish) lens solution that I've yet found.

David

Lennyd- I would go for the Tamron for the IQ and the constant 2.8. You can make up the missing 20mm just by moving your feet and honestly you probably won't even know it's not there. I have owned both lenses and ended up keeping the tammy.
Ken