I'm not sure how it would be for me to be honest, take Deliverance and Isolation Years for example, two completely different songs, still both would be up there fighting for my favorite Opeth-song spot.
It's hard to say.
One thing I must say, and I don't think many will agree, but I think Porcelain Heart was one of the best songs on Watershed, and it's both really heavy and features no growls.
I think that could be a good way for Opeth to make heavy songs in the future, without growls. (if Mikael doesn't want to growl)