Just my 2 cents but I got away from using cat5e for the thermostat and/or sensor runs - I always use the bell wire appropriate for the run. Generally with the AprilAire, I throw the 8870 T-Stats and 8818 Dist. Panel in the mechanical and use the Flush Mount Sensors (I think up to 4 per zone?) where the T-Stat's would normally go.

I have the HVAC guy wire the T-Stats "as you normally would (4wire, 5 wire, whatever)" from the Furnace's to the central location and "you will still connect the T-Stats as you normally would" and we run the sensor wiring (2 wire bell) and handle the control wiring. They do what they usually do, just in a different location and they don't supply the Stats.

Be forewarned - - check all the wiring they install and where they pull it as getting some HVAC guys to do as you ask is like pulling teeth. Same goes if you are not doing the electrical and have to deal with electricians on lighting control. Can't wait for the day we involve plumbers for digital flushing control...