After some time you can fold a Brompton in about 15 seconds. The nice thing about them is that you can take them on mass transit and no one will bat an eye. Regarding your main concern, I had exactly one incident at my former office at 1 Penn Plaza. The security guy told me to go see the manager who took one look at the folded Brompton then inquired as to which front desk joker thought it was a problem.
It seems like you have enough fast bikes. If you're looking for something that can be carried discretely into your office (and other establishments) it's hard to go wrong with the Brompton. It's surprisingly quick with the 6 speed option and great to zip around town to do errands, all without worrying about carrying a chain and lock. If you want real speed, you can order one with Ti parts, slicks, and different gearing. It will cost you a pretty penny though.
...or you can just buy a cheap beater, make it look ratty, and not worry about it being stolen!
David Lam at bfold.com carries a bunch of different folders and that's all he focuses on. He'll definitely be a good person to talk to. Go visit him at his tiny shop at 13th, between 2nd and 3rd I think.