I'm all for mirror finish. My heads and block were damn near mirror finish and I used Fel-Por gaskets. They are leaking yet. I'm sure when I get home tomorrow they will be puking coolant right on the floor now that I typed typed that (thankfully it's Evans coolant so that's only 40 bucks plus shipping a gallon).
I've also finished and ton of surfaces with a stone. And none of those ever lost a Cometic. One was a 300 inch blown gas Comp Eliminator engine. 10:71 blower on gas. He was shifting at 9400 and crossing at 10,200. I know because I've seen downloads from 100 of his runs. Ex Pro Stock guy. Probably the best natural driver I've ever seen.