I went for a ride last night using an RSP asteri 3, a cateye EL220 and 1W LED 'head' lamp on my helmet..
Out of those, the cat-eye was the dimmest, but cast light in a wider area than the other lights.
The RSP asteri 3 was bright enough to illuminate completely un-lit cyclepaths so you could see the path ahead ( I used a section of the Bristol to Bath cycle path to test this from Mangotsfield Station to Staple Hill Tunnel).
The 1W led 'head' lamp, purchased from TK Maxx was almost as bright as the asteri 3, with the added advantage of shining wherever I looked.
All three used together gave best results, although I'm going to replace the cat-eye with another RSP asteri 3.