I think I read somewhere and I think it was from Norbs that low density clefts are usually around the 7-9 grains.
Just an off topic point here, I have a 20 year old GN Ultimate 1000 LE and this bat is/was the best bat I have ever owned... It has only about 6 grains and not overly straight at that... Don't know how GN graded bats back then but being a 1000 LE which was the top of the line back then so only could have been graded on performance.
So after that rambling I don't think grains or density really matter at all.... It all comes down to performance.
I might add that this bat has about 15mm edges and probably a spine height of 45-50mm maybe but rebounded like crazy... Guess you could say it was one of those "one of a kind" bats