You would be surprised.
I've used a few times 5.0 and 5.7 full race sails on my wave board, because I only wanted to switch my IS87 for my wave board without changing the sail (too much chop and too lazy to change the sail as well). It works great. No jumps & wave riding of course, but just blasting around. The race sail tends to hammer the board down. Not bad for control.
IS87 / IS101 / IS122 / US147