Bigger screen is better for looking at maps though. If you're just collecting data and want the odd look at your power/speed/whatever then sure go smaller, but if you're navigating with it then the bigger screen is much nicer and since this is the GPS thread and not the bike computer thread...
It's what makes the etrex 30 unless with its joystick.
I want something that will last a while day, that can then be charged at night. Maybe the 830.
I'd get a etrex touch 35x but I want temperature. Plus ant powermeter would be good