You should tune it down to D, even if there are 10's on it, sounds and plays much better.
Since I can't find heavier strings than 10's here (Belgium)in the local guitar shops, I had to special order them. In the meantime I tuned the guitar down to C. Plays like butter, and sounds good.
I have a middle priced Garrison: http://img223.imageshack.us/my.php?image=garrison12st6.jpg