but is there a general level of wind that a race won't be run in?
We raced in a regatta with sustained (avg) wind of 56km/hr that if you didn't capsize you would finish top five.
Was also at one that same year that was cancelled due to 48km/hr sustained winds. Go figure. The host fleet of the cancelled one was more family oriented, not that had anything to do with the RC's decision, but we sure were disappointed.
So, the rule of thumb may be extremely different for a small inland lake, compared to a bay or ocean, whether or not there is a novice fleet, and what is the experience of the sailors in high wind conditions.