KTM claims you can take up to 10mm from the sub-frame without bottom out worry. Many will also tell you as smilin did, about spacers for the shock which restrict it from comming all the way up.
I am same height as you are and I found that shaving the heck out of my seat foam was all I needed to do. It makes the ride feel totally different, easy to mount, and lowers your center of gravity which is a plus. I used a hacksaw and cut all I could get out of the TOP of the seat. It will make it flat and not a comfortable ride for trailing, But if you MX, I feel it's the way to go before you do any sub-frame shaving.