I have played around with light setups (homemade) different wattages overvolting and mr11 and mr16 bulbs.
the mr16's really do put out more light per watt and there are some great bulbs for them. http://www.bulbsource.net/soluxpricer.htm the 4100k 10 degree bulb is a killer thing. it eats up the power but it is the brigthest bulb out there. I used the 17 degree and it lights 3 lanes up brighter then most bulbs did noe lane.
ovevolting a halogn will give you more light per watt then a bigger bulb.
I use one of these http://www.cs.indiana.edu/~willie/lvr.html#anchor0005 to control the overvolting.