A 600w in that space would give you 37.5 watts per square foot. It's a bit on the low side but possible. You'd just have to keep swapping the plants around every week or so, so they all get their turn directly under the lamp. Or if some plants are taller than others, have the taller ones around the outside and the shorter ones in the middle.

A 1000w lamp would be ideal for that space, giving 62.5 watts per square foot. It's over the 'recommended' amount but your garden would be well lit all over.