I would recommend the quad or triple MR11 LED from cutter. Around 40US$ for three Q4 XR-E leds and optics, makes mounting very very easy(already on a plate so you don't need the extra aluminium). Narrow optic for the road.

MR11 size so you have room inside the tin for the capacitors etc.

The capacitors... the one across the LEDs smooths the output and stops the light flickering. You certainly need this one. The others tune the circuit to help with more light at lower speed. The stuff at pilom.com isn't hard to put together and works exceedingly well. If you're not sure what you're doing stick to the recipe.
I would make circuit 7.