I do 20 and 4 ,While I was in Amsterdam(a trip paid for by growing das weed) this past year I was able to see and talk to a few growers all of them say They have a higer rate of male plants when vegging from seed and a higher rate of hermi's,when growing on for 24. They also say that it Takes longer to veg to size because the roots grow better in the dark cycle,therefore they plant is slower to size. they said 20/4 is better than 18/6 for to stop pre-flowering in some strains. Now I havent grown long enough to test this myself but it was clear to me they had.