I think the speed is highly affected by the population density. I have seen speeds varying from ~40mbps to <1mbps. The less the density the higher the speed.
Which is funny as it's much cheaper to provide higher speeds in high density areas.
How so? Wont more connections to a tower saturate the bandwidth?
Cost of provisioning the backhaul network out to the middle of nowhere maybe?.. and paying people to live next to the tower and top up the onsite diesel generator.