Have you actually seen a Tiger mast break where you were sure it was the mainsheet eased too much? I've seen half a dozen masts break for one reason or another, and there was always something else... spreader failure, mast rotated in, downhaul on, etc. I've dropped the mainsheet on my boat on my N20 and on my F18 and the mast was fine. Plus, we have insurance for a reason, sail the boat fast, worry about breaking stuff when it happens.
Look at this picture of Mischa going downwind at Canadian Nationals... this is pretty much the most you'd ever want it out, his head is just on the verge of twisting off and bleeding some power, the most you'd want to let it out would be another 6 inches, plenty of support still there for your mast.