I have always seen or heard on here that go from less to more if your able to. The plants will love your 600w either way but to save money on electricity you can always go smaller on veg area, especially if its from reg seeds that you are not sure on gender just yet. If I was growing femmed seeds then I would throw everything I have at her without trying to save electricity and go for big growth and faster maturing if possible. I have a switchable ballast so for me if I am out of clones then my babies are first veg from seed on t5ho or cfl then my 400watt mh bulb then switch to hps 400w to finish in flower.