Like I said back in post #4, go to a local shop with a bench, unless you don't have one local; I understand that that is a possibility. I wouldn't get real hung up on the numbers, they are really only generalities and not ment to be absolute.
I know Hughes lists charts of flow up to .700 lift, intake of just under/just over 300 cfm. When you originally bought the heads; do you remember how much power they stated the heads would support?
You stated that you are looking to do a cam up grade.......what do you have now and what are you looking at to move up to?