I believe ZAU is on the same training program. I've heard they've had some people check out in close to one year...from the sound of it it wasn't even 18 months, shorter than that. Which is great since I'll be headed there. While I heard checking out isn't a cake walk at ZAU, that they've had plenty of OTS candidates succesfully finish training there. The people there said it has more to do with your desire than any particular 'skills' you might have.
Chicago TRACON on the other hand is apparently a different story. Someone who works there said they have NEVER had an OTS candidate check out there. So I'm happy to be headed to ZAU.
As far as washout rate for ARTCCs I think it really depends on the facility. I've got a friend at ZLC, and he said it's almost impossible to not check out there. They've only hand a handful of people not make it in the 5 years he's been there. I'm sure it varies at other centers though. It is a level 10, but they still see a fair amount of traffic.