Also, 2007 Cervelos have very short chainstays, 395mm if I remember correctly. They finally changed that and I think they are all at least 405mm now, which is the minimum chainstay length spec'd by Campy. Not saying this is your issue here, but it's one of the things that might be contributing to your compromised shifting issues.
And you are going about removing the cage assembly from the derailleur incorrectly. You do not remove the c-clip. You unscrew the 25mm torx bolts, but be careful to keep pressure on the cage assembly as there is a strong spring in there that will kind of want to do bad things to you
. If you haven't done it before, it might be wise to take it to someone who has. There are actually three different positions for that spring, (there used to be two in 2009 but the they changed it to three to accommodate the new larger 29 tooth cassette introduced in 2010 I believe). Anyway, yes, you can play with the position of the spring and that might help enable you to get the pulleys a little closer to the cassette but I really doubt that's your problem here. I've set up campy drive trains that have more than the 5-7mm space you're referring to and it still shifted fine.
What would be a really useful troubleshooting exercise would be to borrow a wheel with 11/25 or 12/25 Campy 11sp cassette on it and set that up to see if you have the same issues. And what chain are you using, Campy?... or something else. Like @Rmerka said above, when you're mixin' and matchin' it makes it a lot harder to source the problem.
The "new" screw on the Campy 2015 rear derailleur comes from the factory all the way backed out. As far as I can tell it would be used in cases where the rear derailleur hanger positions the derailleur very far forward relative to Campy's ideal specs, and turning it would pull the whole derailleur back a bit. But this would probably increase the distance you are talking about, not decrease it. I've yet to come across an install where that screw needs to be touched.