Hey RedShoe, been watching your project with some interest. Nice one!
I know you're pretty much already done with your project, but if I may make a recommendation?
You might find that a few Luxor LEDs are what you're chasing. They go up to 5W [yes, 5W LEDs] - and their 3Ws are very bright, with a very reasonable power consumption [3AAAs will power them for 25+ hours on full bright]
Everyone is telling you different stories because there are definitely multiple ways to do these things.
Generally speaking though, hooking each LED [esp high consuptions ones such as the whites] to a battery is NOT the optimal solution - most SHOULD have a driver circuit to ensure steady current is delivered. If you can't control the current, you'll burn the LEDs out.
These will not only
a] prolong battery and LED life, but
b] provide maximum brightness off much smaller power supply
Links:
http://www.satcure-focus.com/tutor/page10.htm
http://www.luxeonstar.com/faq.php
Google for luxeon drivers or LED drivers, and you'll find plenty of people have gone where you have before.
I figure if you went to so much effort to make a great device, go the whole way! With a decet driver, you'll have dimming control, and a much cheaper and cleaner system.