I brought home a demo last summer and surfed it for a weekend. We were just using the factory ballast plus about 3 or 4 people in the back. Surfer was a Hyperlite Broadcast 4'9". Granted we are all experienced surfers, but with no additional ballast, we were able to drop the rope and go. Depending on what level you are at, a 5'6" Hyperlite Broadcast may be big enough to surf the stock ballast. Otherwise, look into some of more advance surfers, like Phase Five and Inland Surfer.
Hope this helps!