Average speed is a local metric. As you state, it greatly depends on hills, wind, road conditions, riding partners and etc. Climbing speed is more interesting and is indicative of power to weight ratio. The more your weigh, the more power you have to produce to climb at a certain speed. Humans all have the same type of muscle, heart, lungs and etc. So it is very hard for a heavy rider to produce enough power to overcome a weight disadvantage.

I am 6 feet and weigh 170. I can climb 3 to X mile, 6 to 7% grade climbs at 9 to 10 mph 34/21 or 34/23 with a cadence of 75 to 85 rpm.

How much do you weigh?