At a 5 day national event there should never be a race run in under 5 knots. At a weekend regatta you may be forced to do so in order to get any racing in. At the F18's they have 5 races in, they have a throw out, why have bad races. As far as too much wind. If the chase boats can keep up and everyone is safe, then race. I found at the 16's in CA that the wind and waves together are more of an issue. Also have seen teams from PUR,MEX,BRA,AUS have no trouble with the 20+ knots and big waves.