Every now and then someone will ask me How much does the mizzen add? Yesterday I took carefull notes. The wind was 12 to 15 knots. We were behind the breakwall so the water was flat on a close reach. I had set a full main and our inner staysail. Our speed was averaging 4.6 to 4.7 knots. I then set the mizzen and we averaged 5.0 to 5.1 knots. So... we increased approximately .4 or half a knot for talking sake.
Once we rounded the breakwall and headed out into the lake, we were in 1 & 2's and I unfurled our 135% to add some punch through the waves and we averaged 6.5 to 7.2 knots again at a close reach in the slop.
So... if you wanted to know what performance the mizzen adds, besides balance I would say 1/2 a knot.
Dale
That pretty much agrees with my limited and informal observations - it adds speed and balance on points of sail from a close reach to a running reach. Hard on the wind, it is back winded by the main and contributes little, if anything. On a run, it blankets the main unless I am dead downwind and I can go wing and wing. Actually, it is wing and wing and wing since I put the jib out on the same side as the mizzen :-)