You can get your answers from some freeware software called Radio Mobile. The learning curve is a bit steep so let me know if you would like me to get you some propagation maps.
It is possible to use an SXT at 10km but I suspect that you would be better off with an external high gain antenna at this distance because I would assume that your path would not be perfect at this distance.
You may also be interested in this post because it is similar: http://forum.mikrotik.com/t/some-questions-regarding-a-wisp-setup/74830/1