well, there's width (flood) and depth (throw) to the beam of light.

throw helps with being able to see far
flood helps with peripheral vision


Although not always true, my general consensus for these lights which don't use lens optics
the reflector size (secondary lens) has a lot to do with how the light is emitted.
bigger and deeper reflectors offer more throw.
smaller and shallower reflectors have more spill.

A lot of the P7 and MC-E lights you see mentioned here have a 30mm wide x 20mm deep reflector and that gives something inbetween.

this one, gives amazing throw: http://www.dealextreme.com/details.dx/sku.18475