Welcome to RIU!
I like Discount Hydro, let me tell you why, only place I know that will send you a balast overnite for free the first year you have it (if anything goes wrong) and they have a free catalog they will send you full of good info
http://www.discount-hydro.com/
as for the 600 watter can't help I like Ceramic Metal Halide's (only get up to 400 watt)