Just a couple thoughts on cycling rain capes.

1. Be sure the cape does not block your lights.
2. I think a cape with finger loops (or something like that) is better than one with a clip that attaches to the bike (watch for ponding between the hands/arms).
3. An inner waist belt for the back will help keep the cape from sailing.

I have a cheapo Monkey King nylon bike cape from ebay that I use for heavier rain and it has problems on the above three points (but only cost $8.)