There are two or three different levels of carbon in the Fs and Zs, but the geometry is the same down the line.

I had an F5 that was really a terrific ride. Quite stiff, maybe a little wooden, but smooth with stable and predictable handling. The F cockpit geometry is long and low, though. Some lanky body types may not be able to get comfortable on the F. It's like a Trek H1 with a longer top tube.

The Z is another story, shorter, taller, longer stays, but still quite snappy for an "endurance" geometry. If I were considering a Roubaix I wouldn't hesitate to buy one of these instead.