Have not used the IBS when boarding -- just the KGB and about 350lbs in each rear locker. The 205v/X2/X1 hull throws a mean wake for boarding with the basic stock ballast.
For surfing I use IBS, KGB, and 750lbs on port side, plus a couple of people on port side.
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate, custom wake shaper
(previous) 2001 X5, 1991 TriStar 190