We talked about this a lot already, and we came to the conclusion that it would be less expensive to have a "small" linux server.
I've found out that to be able to get to speeds like the ones in Windows we need at least 1.2/1.5Ghz + 128Mb RAM + openwrt.
I've currently installed a "NETGEAR Nighthawk AC1900 Gigabit Router" in a cyber-cafe that has 40 to 60 people connected at the same time, this router is permanently connected to Franfurt-Cantus (this way the person that owns the cyber-cafe doesn't need to worry about what people do in the internet), and on the day of installation, I got 40/40 in a 100/100 Fiber-Optic connection, I was quite happy in the outcome of this but I will check again later this week if there was any downtime, mostly problems with the dnsmasq + dnscrypt (I got those a lot).
So just saying, if you want a very good router think in 200USD for this one, if not you can get a lot of those dual-core 1.2Ghz mini-tv-pc for 100USD just be sure it runs linux (because a lot of them only runs Android).
I'm currently also starting a project for the new Raspberrypi 2
it seems that it can get a lot closer to those "small" linux machine for 35USD
we will see.