swapping 3 600's for 3 400's hps

iv got a space about 5ft by 7ft roughly 8 or 9 foot high, i currently grow 20 plants in this space with 3 600 watt hps lights , but im thinking of getting some new 400 watt lights, would this make a difference or would they be just as good because its a small space??? Cheers

400 watt=55,000 lumens, 600 watt=95,000 lumens think about it...

don't do it...
600 = most lumens/watt