I recently bought the Sigma 24-70mm f/2.8 lens but wasn't happy with the lens so I returned it back. It was too soft on the 70mm end and zoom ring was way too stiff. I would like to replace my 28-135mm f/3.5-5.6 IS lens for a faster lens. I already have the Tamron 17-50mm f/2.8 lens and I love it. I need a walkaround zoom lens like my 28-135mm but I need a larger aperture. the extra 20mm from the Sigma did not cut it. I need more focal length. I am looking at the Canon 24-105 f/4L lens but the aperture is not large enough. Any suggestion as to what other lens I can look into? This would primary be used for weddings and debuts. I don't mind third party lenses, but would rather stick with Canon lenses.