I have a full Canon system too so I can share some insights.
The 24-70L is a very good lens. VERY fast AF. It instantly snaps into focus, faster than my DA40. I haven't had any focusing problems. Sharp and well-built, the zooming action is very smooth. Overall a very well-balanced good zoom. The new Nikkor 24-70 kicks its ass though (seriously that lens is disgustingly sharp)
The 16-50 is a very good bargain zoom. For about $600 you get full sealing, great build and f/2.8. I got a very good copy which was very sharp in the middle, but the corners were a bit weak (EDIT) wide open (EDIT) . I loved the focal length range, having 16mm was awesome, I didn't miss my UWA much. The zooming action is not as smooth though. Contrast is very good and colors are punchy, contrastier and punchier than the L lens. AF is slower than the L lens.
Best zooms out there IMO are the latest Nikkors (14-24 and 24-70), blistering AF, amazing build, optics even outperform some of the best prime lenses out there. Seriously. But they've got serious price tags too
Back to the Canon and Pentax lenses, both are great lenses, as long as you know their limits and their price tags.