New Grow Room

Im planning on using a 400w in a budbox xl for 8 plants im pretty scared that the lights not enough and theat i wont get and lower light penetration.what do you guys think should i buy a new reflector and a 600w or can i use a 400w with cfl on the sides i will have pics of everything soon,

a 400w is good for about 3x3 feet if that helps