Look for the BOMM protocol on gotmead.com. A number of different beer yeasts were evaluated, and by far the best result was obtained with WYeast 1388 (Belgian Strong Ale), the Duvel strain. With this yeast you can go to 15% ABV without having to use chemicals by using the step-feed method (let a mead ferment dry, and then add subsequent small portions of honey until the yeast chokes).