I haven't studied the 2013 Z's and how they may differ from mine. I've been riding a Z for 2 or 3 seasons now. (ZC frame which I built w/ Sram Red and other parts and wheels I already owned). I have loved that bike since day one. It's comfortable and light weight, yes and very fun to ride. But what I notice over my old bike (Cannondale CAAD7, nice bike) was that I actually go faster down hill. It's just more sure feeling to me. Probably the longer wheel base, and maybe some more compliance to the road. (Same tires and wheels). Oh, and I can get down just as low in the drops of my Z as I could with the CAAD. Just a very minor adjustment in elbow bend.
I imagine there's a million excellent choices in that type of frame, but the Felt Z is one of them for sure.