yes. i have a 400 watt in a space thats 2x3x4 and it works lovely im sure the 600 watter will be fine and a good 6 plants in that area should work wonders for you.
i personally recommend a 600 for a 3x4 space, i know adverts say its good for a 6x6, even 4x4 for a 600 just may be perfect, your plants on the outer edge of the lights footprint wont get much so rotation may be perfect for your scenario