My thoughts are that I would try and grow them tall rather than short and bushy.
Would I be wrong to think this?
The tallest you want your plants to reach in bloom is equal to the maximum
optimum depth (downward distance) your lighting is capable of minus 1 foot (approx) for the space from light to plant. I know that might sound a little confusing so I'll explain.
With a 600w HPS (and for this example) we'll say 5 feet is the maximum, optimum depth for this light. Remember, we're talking about a straight, downward distance to figure out a maximum plant height. (Personally I would only go 4 but I'm a real stickler for maximizing optimum.
Some might even go 6 but that's pointless with a 600w in my grow book.)
With that 5 feet, we have to subtract 1 foot for the space between the light and plant. I don't think I need to explain why, but I will say that the 1 foot is approximate, depending on how good your ventilation is and whether or not you're using a cool tube etc. The measurements don't need to be precise anyway; I'm just trying to give you a decent example.
This leaves us with 4 feet as the maximum height we want our plant(s) to reach in bloom. With that in mind you can decide how tall you should grow the plants in veg before starting flowering. It helps a lot if you know the strain (have grown it before) but you absolutely have to remember that your plants will at LEAST double in size during bloom. With a 600w they will more likely triple, and if they are Sativa dominent could even quadruple. If you use 'triple' as your guideline then the plants should be vegged to a
maximum height of 16 inches. (3/triple x 16 inches = 4 feet.) Personally, with a 600w I would not veg any taller than 1 foot to maximize bud production from top to bottom, but that's up to you.
Taller is not better unless your lighting can handle the height; otherwise, you're simply wasting time. Hope this helps.