The Osram Rallye 70/65w +50 H4 bulb at
http://store.candlepower.com/ would be my first choice without upgrading stock wiring; this is sometimes sold as a Philips bulb. I have them in my car as well as on my bike. Osram makes a higher wattage bulb that is available through Candlepower as well but I wouldn't chance toasting the wires (even as small of a risk as it is). I considered going with a heavy yellow tinted bulb for the advantages in poor weather visibility but was recommended by two separate companies to NOT do this unless I were to go with a ~100W+ bulb and stock wiring.
In my experience PIAA is absolute crap. Sylvania (the Silverstars in particular) were great for a while but, like PIAA, they seem to be targeting fads over quality lately. The bottom line with incandescent bulbs is that without going with a truly higher power consumption, you will not be seeing any major gains in light output if you stick with a major manufacturer. The X/X watts = X/X watts ratings are a gimmick, and almost all tinting will reduce output. This is why I like the Osram bulb; it is one of the few bulbs with a white color, slightly higher wattage, and not a high enough wattage to require relays and new wiring.
I think Candlepower is associated with Daniel Stern Lighting, which is an excellent source of information regarding automotive lighting. More about cars than bikes, but the information is still valid.
