6km Wireless link speed?

Hi

I have an 6km link on two RB800 running R52hn both sides with an 27dbi 5Ghz grid bith sides, I get an Link of -74 and 60%CCQ?
When I do an bandwith test I get bout 37 - 40Mbps, is that the best it can do? I am running it in Nstreme? Any advise on how to increase that speed?
Im running in N-Only mode and noise of -110.

Hi,

Do you have clear LoS?

If you have clear LoS then -74 is not good for 6km with 27dBi Grid.