Practical Sailor looked at this about 15 years ago. They were trying to understand why there had been an inordinate number of mast failures connected with boats sailing under jib/genoa alone. I don't believe there was any distinction made as to fractional/masthead rigged. As I recall, the only pattern they found was that the vast majority of boats that experienced mast failure while flying headsail alone had one common aspect to their rig geometry: Single, rather than double, lower shrouds.
Thatís interesting. Do you remember a year or anything else I can use to track that article down? A mast with a single lower is weaker then the same mast with a double. So if everything else was the same I would expect to see a greater number of mast failures in the single lower rig no mater what the working sails were. I wonder if the article has numbers for the number of failures when both sails were up compared to when the boat was just under a headsail. Do more spars fail under headsail alone then under main alone? Also do more people sail under just the headsail because roller furling is so easy? If a backstay breaks the rig would fail no mater what your choice of sail was so looking at the cause of failure might be worthwhile. Did they do that in the article?
All the best,