I went to Cometics after pulling leaky RJC's off my car. It shouldn't take a paint roller worth of silicone to seal a headgasket. (much of which finds it's way into places it doesn't belong.)
A Fel Pro or composite/paper gasket shouldn't need any sealer, EVER.
Steel shim gaskets will sometimes have a paint/laquer coating on them that helps seal.
The Cometics are a loose 3-layer gasket, riveted together.
Put them in the sun and watch them distort and bend as the temp change makes them expand and contract. I ground-off all the rivets holding my Cometics together and smeared a thin layer of black RTV silicone around all the water passages. I did this to the block, heads and all layers of the gasket.
I used ARP studs, torqued to 80ft lbs.
Another VERY important thing I think many forget, overlook, or just don't know about... USE A LOW PRESSURE RADIATOR CAP !!!
Go to the local auto parts store with your factory 20+psi radiator cap and match it up with something 7-10psi. Buy the lowest pressure cap you can find.
Most guys run 160 T-stats in the cars anyway... so the water never gets close to the 212f boiling point that requires a high pressure cap. (For those that failed science class, pressure raises the boiling point)
The weak link needs to be the radiator cap... NOT the headgasket. Consider the low PSI cap a "safety blow-off valve" if the car gets too hot.
I'd much rather see my car puke the coolant out the overflow... instead of pushing it past the headgaskets.
I've been doing this for 25+ years... and it's standard practice on high-end race motors running copper gaskets.