Mikrotik SXT PTP low speed link

Hi, I have 2 Mikrotik SXT devices.
Configured them like this:
http://www.wispforum.net/entry.php?5-How-to-Connect-two-Mikrotik-SXT-5D-s-In-Bridge-Mode-Part-I
http://www.wispforum.net/entry.php?5-How-to-Connect-two-Mikrotik-SXT-5D-s-In-Bridge-Mode-Part-I

The devices are about 250 meters from each other.
Now I have a linkspeed upt to 6Mbps.
Verry slow.
How can I get it faster and tune it?
I’m new in RouterOS.