I had a feeling someone would chime in with a response along those lines regarding tension but I wasn't 100% sure. However, if you overtension both sides, the mast will be pushed downwards into the boat. Most of the time it's fine but not all boats are built the same. The 420 I had as a kid (I pulled it out of the trash) had a bent mast and stretched out stays. As far as I could tell, it sailed just fine but then again I was only 13 and had only sailed on dinghies. I'm not sure what your sailing experience is but the best lessons I ever got were capsizing lessons. I rarely get nervous on the water.