Fuck sake! Here we Fucking go again. Fuck, its like i say. You know Fuck all about me. But am Fucking finding more and more about you. You know Fuck all about where i live, or my Fucking grow. Cheers for the neg rep. Much Fucking appreciated.
Dont know about us prices, am in uk. I would go for the 600 mate, out it of all of the hps lights it is the most efficient. 90000 lumens for the 600, 55000 for the 400. The price difference between the 2 is very small. Makes sense to go with the 6. What size is your growing area?
You should check out the cool tubes that take 2 lights. Buying it as a complete kit with fittings and ballasts, will save you money. I grow between 5 and 9 plants under my 600. Alot will depend on how long you veg for. You would fit alot more if you went 12-12 from seed. Which i do not...
Yeah mate you can use both types in line with each other, think its up to 4 with one rvk 125a1 fan. With the space you have i would be tempted to go with 2 600s in cool tubes.