Danny, there are some tech shops specializing in Subies that have pretty much licked the head gasket issue using other companies head gaskets. I read this site below comments years ago and I think they use six star but there are other companies as well.
I do not think the issue is not as prevalent today but cavitation is a problem if coolant goes from a liquid to vapour it looses it's cooling effect. Using Evans coolant helps too as it does not go to a gaz state so it can continue to cool the head.
Others ways to prevent flash heating the heads seem to be to make sure you idle for a bit after a hard run. The extreme guys have a circuit that runs the aux pump until the temp drops.