Desmondpun,
It is certainly posible to mod the C3 with a 5W but given the thermal considerations as well as the beam you get with the P reflector and a 5W, I don't think the work is merited, IMHO. You also would either go for a direct drive or need a buck converter. I have seen the KL5, first hand, and it is the best deployment of a 5W LED I have seen so far. It has a great spot/ flood combination beam which can't be obtained from the stock reflector or optics. Short of going to a turbo head (what Darell has) or other large diameter reflector, the KL5 is soon to be the new standard! Of course if you go to a M3, the KL6 has an even larger diameter so its spot is even tighter.....
I suggest you hang in there and hope SF brings the new KL series to market soon.
- Don