It depends, I used 4x 240w for 9 plants in a 5x5.
Now I like space so I can get in with the plants to maintain them, with 9 plants the doors open and light and smell spills out, I don't like it.
Now I put 6 under a 750w bar light in full flower using 3.5/4ft square sectioned off.
They're under a 400w mh atm in 2.5 x 2.5ft I'll swap it to the 750w bar light when required.
The difference they reflectors make is considerable, 20% at the wall and 7% in the centre.