I currently have a Cateye 320 (don't laugh) and have ridden my 12 mile commute in pitch darkness through the sticks with it at 19mph average and found it ok (but I know the road and where the potholes are).
My LBS leant me a Lupine Wilma with 920 lumens and a L&M Seca with 700 lumens two weeks ago to try out.
Damn they are bright, and damn they are expensive! Obviously they pale my Cateye into insignificance.
However, I have to query how much of that light for road cycling is pointless. I am only interested in being seen from the front, being able to see where the road goes and most importantly what the road surface is like for a short distance infront of me.
I am not interested in seeing the trees that line the road for 300 yards or the immediate 30 metres infront of me looking like daylight (would be cool for £50 but not £400).
By way of comparison I rode home the other night in the dark using a Surefire Scorpion torch strapped to my bars (this is an oldschool tactical torch knocking out 78 lumens).
Yep it was on "spot" but the three things I needed to accomplish were easily done.
I am now looking at either a P7 based torch/light or more than likely a Hope Vision 1, which is only worth the extra £30 due to the fact that the build quality and UK service from Hope is supposedly top notch.
Surely lights for £200 plus and especially £400 plus like I have been testing are total overkill unless you are riding of road? I would however never say "you have wasted your money, you should have got a P7" like so many do on forums, especailly Bike Radar. If you have the money then why the hell not spend £400 plus on a light, that's up to you.