more watts just means more bud, it wont happen any quicker though. just get as many watts as you can afford, space is a determining factor.
if you put a 1000 watt lamp in a 2 by 2 foot space you could be in trouble as they produce shit loads of heat, then you start getting into ventilation issues, and you may possibly burn your house down lol.
if your growing ten plants two 400's would do nicely.