first off.. dimmable ballasts.. only work with whatever size bulb it runs at 100% .. then u can dim it down to use less.. but u dont use a smalller bulb.. atleast thats wat i was told.
have you already been flowering or are you just about to flower. I would say the 1k if you are just starting to flower and then switch to the 1k hps. but if you have already been flowering I would stick with the 600 w hps because they will really need that red light out of the 2700k bulb. also I guess it would depend on how many plants you have
yeah i have a 600w dimmable ballast that mean i can only plug up a 600w yet it has 4 settings 350,400,600,650 I hope you dont put the 1k in a 600w ballast put up pics of your ballast
I use 400 Watt bulbs every summer with 600 Lumatek Digitals , of course they are set on 400 and all is well .. Been doing this for years and I use the bulbs for two summers , then they are disposed being that that is about 6 months use on the bulbs ..