Looking at some of the photos of that type of LED setup they are rather good.znomit wrote: The mr11/16 replacement units are not bright enough and have poor efficiency anyway. You really need a new housing because halogens like heat and LEDs hate it. They aren't hard to build. Bikeled.org is a good start. Candlepowerforums and MTBRforums have good bike light sections.
For a 35w replacement you want three good LEDs at 1A.
Good stuff here
http://www.cutter.com.au/proddetail.php?prod=cut757