Hello we have several links of 38 and 41 Km, then we are here on the forum Mikrotik so I'll recommend these products and not others
First of all I have not yet used the new models MT Netmetal that a reading of their characteristics are certainly the most appropriate for long links with high data transport.
Our experience on link of this distance provides for the use of:
2X RB911/912
http://routerboard.com/RB911G-5HPnD
2X mAnt30
http://routerboard.com/MTAD-5G-30D3
With clear LOS you can get a throughput between 20 Mbits and 40 Mbits full duplex,
cetalfio