too much light?

£100 gets a 400w/600w hood bulb and ballast

ok... 400 or 600 watt whats betta 4 my 6' grow room

400 is your best option with an air cooled hood and get some mylar to put up on the walls.
you could put a larger light but really the only advantage you might gain is better light penetration and disadvantage of added heat, electricity usage etc.
a 400 does a good job on smaller plants and if you can have a seperate area with cfl for cloning or keeping a mother a sog or scrog will probably yield the best as it keeps the canopy even and close to the light.

thx bejay