Last night I got the z51 swaybars on, and wow they are huge compared to stock. It took me a little over an hour to install these, all the bolts are super easy to access, great design.
C6 Base: 25.5mm front, 17.5mm rear
C6 Z51: 31mm front, 25.6mm rear
Here you can see the original rear bar at the top, the new rear bar, and the new front bar which is huge:
Here is the old front bar compared to the new front bar:
Unfortunately it's raining today so I haven't been able to test them, but everything I've read says they make the car feel more planted. Maybe I'll get a chance to test them out this weekend at the autocross in Marshalltown.