On the standard head hasket, SOUTHAMTON UNIVERSITY were having to do head gaskets on STANDARD BHP engines when the did the NVH testing for FORD/COSWORTH.
Standard one is not worth having really even with standard power.
A group a one YB 0611 will cope most say up to around the 400bhp mark, and is FIBROUS so a very good one, as it will cope with any slight imperfections in flatness of head/block much better than meatal ones.
tabetha