Sounds like our neighbourhood, except its 15 years old... still very little trees and we do have some elevated terrain (a small hill) in it.
We have one A5-14 running with 60 3rd party (Mikrotik SXT-n) clients and we offer them up to 50Mbps.
So far it runs absolutely fine! Before we've had two Mikrotik AP's serving the same in tdma and clients had 25Mbps max but regular comments about slow internet.
Now this AP's client base is silent, everybody seems to be happy. We see top usage of 60-80Mbps downloads to clients where most of the clients themselves are allowed to use up to 50Mbps in burst.
But like you already stated, we rarely see a client using more then 15Mbps by itself.
We know we have clients using IPTV (including myself) and playing games or making Skype calls and it all seems to be working fine.....
On the moment we are changing al 'n' SXT's for 'ac' SXT's so we can try to work in 80Mhz channel (or use the higher modulation in 40Mhz) and see how many clients we can really serve before the A5 starts to crack.... Only after that we might go for the extra mile in huge investment in 60 or more C5's....
We are so happy with the present results already that its hard to explain the extra investment in C5's to get the extra speed that in fact nobody asks for.
Clients pay only 25€ per month so the ROI half a year at least where same money better be spend on the expansion in more Mimosa AP's in the rest of our network. (we have 20 AP's with even so many backhauls to feed them for some 700 clients. Our budgets are very limited hence the priority..)