I was thinking about getting a 1000 watt but Im not sure if its worth it. Will I notice a "big" difference growing with a 1000 watt over a 400 watt. I only have space to grow about 4 big plants so Im also wondering if a 1000 watt is over kill...
How much space? Generally your plants will put that extra light to good use, as long as you have the height to maintain a proper distance (which will be more with a 1k light) and can manage the extra heat. Not only better growth on top but better light penetration for development under the top canopy.