Originally Posted by
rm -rf
The garmin 705 has an optional cadence + rear wheel speed sensor, so that will work on a trainer. (If you don't have the sensor, it uses GPS to calculate your speed, which won't work on a trainer, of course) This would be the same for any garmin with a cadence+speed sensor. The rear wheel speed sensor is more accurate than the GPS, too.
The 305 also has an optional cadence. When I upgraded my 305 to a 705, I used the same cadence sensor. The appeal of the 705 for me was that the display is high def compared to the 305. I also ride at night and the backlighting on the 705 is much better.
With that said, if I was in the market for a new Garmin, I would probably go for the 500.
I also don't like the idea of a touch screen on the 800. The buttons on my 705 work well. I see no reason for a touch screen.