I'm heading to Canada in a few weeks time and I'm thinking about upgrading my kit lens to a Tamron 17-50 f2.8. This is available for around £330 which is a fair chunk to pay out for the constant aperture. I mainly shoot landscapes so I was wondering if the upgrade is really worth it, seeing as most of my landscape photos will be shot at smaller apertures than wide open (i.e f5.6-8) which both lenses can achieve stopped down? Does the Tamron achieve much better results over the kit lens at this range?