My 500 definitely has avg speed. Lots of other stuff you can add to customizable display pages. The owners manual https://buy.garmin.com/shop/store/manua ... 28&ra=true
" onclick="window.open(this.href);return false; has a list of data fields starting on pg 38.
Altitude, total climbing, and temperature are the things I've noticed to be fairly inaccurate. A typical 27 mile climb for me might show 3089' when a mapping site like ridewithgps shows 3494'. I think I read that it uses barometric pressure for altitude; not sure what other units might use. Temperature is wildly off - can show 20F higher than actual. Manual says this "may" display higher than actual if unit is placed in direct sunlight, which amuses me a bit - where I ride I'm almost always in direct sunlight.
Overall it satisfies my limited needs. 18 hours of battery life specified is pretty accurate - I've had mine running for 12-13 hours and showing 35% remaining.