I went for a sail in my 6 tonner once without trimming ballast (approx 1/4 ton) on board; the difference was quite amazing - she didn't feel anywhere near as stable.

Draft should be about 4'8", so floating 6" above her marks is about right. You probably need about another 2 tons in her, as she would have had big steel water tanks in the bilge plus some pig iron trimming ballast.

When adding ballast, make sure all tanks are filled, and all cruising gear on board (personal gear, dinghy, sails, anchors and cables, etc) - this will set her down at least a full inch, and also goive an indication of whether she needs trimming also. Remember to leave her slightly light at the stern (about an inch or so) when nobody is onboard, so that she comes level when you have a full crew in the cockpit.