I listen to the person I use, with his 54 years experience including building engines made/forged bit by bit from the ground up, has his own dynos, etc all the machine facilites you could ever think of, builds many many succesful engines, last year one costing over £100,000, had many one off components, was some historic engine, for someone richer than me!!
Plenty of norweigan chaps running 500+ on group a, they seal better due to thier fibrous nature on non perfect surfaces, ie where block has not been skimmed.
tabetha