I wouldn't expect the 35 to do noticeably better than the 17-55 when both are at 35mm and f/2.8. If you look at photozone's APS-C analysis of both of these lenses at 35mm and f/2.8, you'll see they show the 17-55 having better MTF50 both in the center and edge of the frame. It's just that good. I compared my 17-55 at 55mm f/2.8 to my 60mm f/2.8 macro, and while the macro was the clear winner, the 17-55 still surprised me with how sharp it was wide open.
It's something of a misconception that when you pay more for the L glass that you're necessarily getting the sharpest lens. It's not true for the 50/1.2 either. What you're paying the big bucks for is super fast big lens elements in a tanky package, not super sharpness. Case in point, the 60mm macro is easily the sharpest lens in my kit, and it's the cheapest (it was $390 and it's in a bag with 3 other lenses in the $1000-$1500 range, two of which are L's).