For straight SOG...as in single cola plants.....I just use 4" cubes set in 6" plastic pots, 32 in each 2x4 tray. I flood to drain twice a day and have 1 minute cycles every 3 hours to keep the roots that grow out the bottoms moist..... I tried filling the pots with hydroton, but it's a PITA.........it floats, it isn't all that easy to clean and I seemed to have way more bug problems with it than without....so I ditched it all and just stick with the 4" cubes....... Never tried the 6" cubes as they're way higher cost than 4".........I guess it just depends on how big you let your plants get.........mine veg to 8-12" then bloom to 24-30".......1-4 tops right now, but will settle on a specific # in a few months......seems best with only 1 or 2....but I'm experimenting with 1,2 and 4 to see which is most productive for me....... The point is...unless you're growing shrubs, you can get away with 4" cubes just fine...........