My veg room is about half the size of my flower room. So that should give you some size comparison there.
Since you are using 600watt lights, I would suggest making your grow area like 3'x6' instead of the 6'x6' area. The 600watt lights just wont cover that entire area. I use mine in a 4'x4' area, and I am about to stick a second one in there.
Also, with 600watts, you will not want to flower your plants at 2ft tall. You could end up with some 6ft plants, and that is just no good for a 600watt light. Shit, its no good for a 1000watt light. You want you plants to finish at about 3ft tall. So depending on the strain, this could mean flowering at anywhere from like 10"-18". At 24", I would guess you will be well above that 3ft mark, at which point they will be taking up so much space, not getting enough light, and just causing so many problems that the yeild will not be increased, but rather diminished by this.
My veg chamber is lit by 200 real watts of CFLs. You will need like twice this since you are flowering more plants. You would probably have better results with a 250 or 400watt MH instead. There is no point in only flowering 8 plants if you are using 1200watts. I am flowering 11 plants right now in my 4'x4' area, and the "footprint" they are grown in is only 3'x3'. (I have an extra foot just so I have room to move around and what not.) You can flower like 18 plants in there, not just 8.
The main thing to remember is, just because you have tons of lumens coming from the best lights, the best nutes, all the best equipment, does not mean you will have the best harvest. Its more about the grower than it is what they are using. An experienced grower with out yeild a newbie and use half the light. Plus the buds will even be better. You can't buy experience. And that is the key to a successful harvest.
I would suggest starting with a single 400watt light for flower, and a simple veg cab with like 200watts in it. Once you get this figured out, and you are getting like 8oz of killer herb, step up to a 600 or 1000watt. There would be nothing worse than spending $1000+ and ending up with nothing but dead plants!