This depends on how much you value your safety and how fast you want to ride in the dark?
For me, I remember the days of the days of the wonderlite that probably put out about 10 lumens at best.. Now when I ride, I have a P7 and Q5 thrower in addition to a helmet light, all total around 700-800 lumens.. I consider this optimum for my safety on the road..
I would recommend to use the turbo mode, get some good nimh batteries and carry an extra set just in case you need them..