[CalebD]

Coil. Definitely.

Also make sure you are running your engine "room" fan and that it is working efficiently. 4 hours of running puts a lot of heat into the surroundings in the engine room. I believe that the problem is that the coil can "overheat" and no longer produces sufficient spark at X degrees and has to be cooled off a bit before it will work again. The better your engine room circulation the less likely this is to be a problem.
Experienced this coil issue on a Tartan 34' under similar circumstances. The engine room circulation on that Tartan 34' was compromised imho, hence overheating eventually.