Dear all,
This is my first post, I hope to gather a lot of interesting answers! 
We are a Spanish integrator and we frequently install Mikrotik devices in Hotspot configuration for hotels, schools, etc,… For Small to Medium sized environments we go for the RB850 and for larger ones, to the RB1100 or CCR1009. This speed limitation problem is happening with the RB850: we connect it to a 300Mbps Fiber, and we get just 160-170Mbps from the Ethernet LAN, as the CPU goes to 99,99% In the real scenario, our customers normally limit the speed to the guests to 5-10 Mbps and we are used to see these RB850 handling up to 100 simultaneous customers with no problem at all, but last week one customer wanted to test the Mikrotik with cable and we realized that there was a limitation.
In the beginning I thought that the CPU was going up because of the Mangle, but I eliminated all Mangle,QoS and Qeues and the problem was still happening. Even if I ake an IP binding to bypass the MAC of my PC, still the CPU goes high. BUT, if I disable the Hotspot Server… voilá! 300Mbps and the CPU gets UP to 80% aprox.
I have used the Tools–>Profile and a big % is going to the Firewall, even if I am not using it or filtering anything. Maybe the Dynamic rules created by the Hotspot are making this CPE go so high?
Any clues? I think that the RB850 should have enough CPU to handle a peak of 300Mbps some seconds. If our customers see with a Speedtest that the Mikrotik is reducing a 40% their total Internet capacity, it will be difficult that they trust on us.
Any tip would be very appreciated!!