That is the size I'm gonna run on my 400. I friend had some 20x11x10 S.T.U. Sand Skate II's on his 250R and they worked great. My tire setup will be 20x10x10 Skat Trak Edge on Douglas Ultimate Billet center wheels and Skat Trak Mowhawk fronts on Douglas Ultimate Billet center wheels. I highly recommend Skat Trak tires. Best paddles I've ever used, well worth the extra money.
I would recommend the Sand Skate II's. This type of paddle tire has the Angled paddles which hook-up good and seem to turn and slide better than the staight paddle type. Most people I know and see use this type and really like it. Down side is that their not cheap. The other type that's close to it and cheaper is the Sand Shark which is made by GBC.