600 Lumen is the limit for most DOT and CE road use lights and the only currently available LED capable of that is the new SSC P7 emitter shown below.
This LED is proven reliable and is being used in other commercially produced lighting products. It's capable of 900 Lumen so it's not being driven to it's rated capacity making it even more reliable. Driver circuits are also available using standard current regulating chips and are reliable as well. Considering the quality products Cygolite sells I would have no problem at all purchasing one.
If your a DIY person and want to build a new P7 light I'll save you a little search time.
Complete reflector, heat sink, P7 emitter, and driver circuit.
The above driver is a simple 1 mode full power circuit. Personally I would order this 3 mode driver circuit for reduced power consumption using lower power modes thus extending run time. You can also be nice to others and not blind them.