All shots done with the camera/lens on a tripod, with remote shutter release and mirror lockup.

A Tamron lens calibration tech once told me that even through the Tamron 28-75mm f/2.8 lens is called a "macro" lens, that it isn't a real macro lens. With the consequence that if they adjust a 28-75mm so it has spot on focus at short distances, then it won't be spot on at medium and larger distances. Hence, testing by shooting the lens box (short distance) is ill advised.

I *think* that these tests bear this out. Both lenses did poorly when shooting the Tamron lens box. And did marginally with the "Tim Jackson focus chart" test. But (IMO), both lenses were excellent shooting the small toy boats, with a slight edge to the Canon 17-55 IS. But in all cases, any slight softening at f/2.8 can be dealt with with a slight amount of sharpening in PhotoShop. IMO.