hope this helps somebody looking for a new lens.
Tamron SP 24-70mm F/2.8 Di VC USD versus Canon EF 24-70mm F/2.8L USM versus Canon EF 24-105mm F/4.0L IS USM: Part I
Tamron SP 24-70mm F/2.8 Di VC USD versus Canon EF 24-70mm F/2.8L USM versus Canon EF 24-105mm F/4.0L IS USM: Part I