In the discussion about RS800cx on Slowtwitch user wvarta.PolarRep provided more details about the Polar RS800cx. Here is a copy of the text.
RS800CX is a nice upgrade from the RS800 if you are active in mutlisport (numerous sports) and even tri. I have to admit, I do not have a BETA/ test unit yet and did not get a chance to try one at a Polar function, so I lack some of answers to ALL OF YOUR QUESTIONS. Essentially it is the RS800 that when used with the G3 GPS will do a post run plotting of your route via Google Earth. With Polar Sport Zones and the colors associated with Sport Zones, your route is outlined in the color your Sport Zone. No uploading of a routes pria to run like Garmin. RS800CX can hear a WIND Speed Sensor from the CS600 as well as the Cad Sensor. RS800CX will not work with WIND CS Power Sensor, don't ask me why, but could be that the that the watch is RS based not CS and speed it speed and maybe they factored in Cadence with existing cadence feature??? Since I do not have one, I have not field tested it from BIKE to RUN so PLEASE hold off on these questions. Once I field test one, I am more than happy to post my experience. Still uses Protrainer 5 sofware which is more informative than Garmins Training Center when it come to REPORTS and plotting of time in zones, distance per sport, total time per sport etc. Garmin still has an edge when it comes to not getting lost via a route loaded beofre a workout, that is their specialty and HR and training is ours. Hope this helps some of you. Disclaimer... I WORK FOR POLAR