I have clients getting 12mbps at 5 miles on 10mhz channels so I would think yes you should get better speeds.
Are you running the bandwidth tester as both or receive then send.
On the link I just tested the BWT show 12mbps send or recieve but on both it's 5.9mbps RX/TX.
Is the link a PtP or PtMP?
If it's PtP have you tried Nstreme?
You can also try unchecking the supported data rates of 54,48,36 on each side. Some times it helps to run the link slower so that it doesn't bounce up and down.
What antennas, router boards and radios are you using?
How high are you over the trees at each side?