Here's my EOS and Zeiss Family.
I use the converted 17-35 on my 1Ds, the converted 24-85 and 5D is a perfect match and the converted 70-300mm and the 1.6 FOV Rebel XTi body are ideal for me.
When needed, these zooms come off and primes are used as needed. But other than large aperture primes or tele primes, I seldom need to use anything else for my photo needs.
The 17-35mm f2.8 blows the Canon 16-35L away. Image quality is simply superb and the Zeiss colors are hard to beat. Tests at a couple of web sites did the usual run down and the Zeiss 17-35mm was only second to the CY 21mm f2.8 (which was expected with the prime).
From what I understand, the 24-85mm is actually a bit better than the CY 35-70. It is much better than the Canon 24-70mm f2.8L except it is not as fast. With the 5D, it is the ultimate walk around lens for me.
The Zeiss 70-300mm was enough for me to get rid of my Canon 70-300mm DO IS and 70-200mm F2.8 L lenses. I do wish it had a tripod mount on it though as it does not balance too well and is quite heavy.
The converted Zeiss lenses actually seem to focus a bit faster on the Canon 1-series bodies than they did on my N1 or NX. To me, it is well worth it as the image quality is hard to beat.
Also, here is a comparison (size) of the Zeiss 17-35mm f2.8 N mount and the Canon 16-35mm f2.8 L Mk I. What gets to me is the cost of 95mm UV or Circular Polarizers. I already had a Contax 95mm UV filter. Recent prices on the Contax CP-L (if available) is around $450. B+W's are around $300 - talk about expensive. The hood, if you have one, is a rare find - harder to find than the lens itself.