i think everyone has their own preferences as far as headlite and fog lite bulbs go. endless discussions as to whether yellow or white bulbs are better in fog. my own experience is that the piaa H4's over time, coat the inside of the headlite lens and the relfector with the coating that is on the bulb itself. i removed the bulbs and compared them to brand new ones, and found the coating (blue substance) to wear off over time. also had a few explode, which according to piaa, was caused by too much heat buildup in the headlite housing itself. they did replace the bulbs for free.
i tired hella H4's with a yellow coating, which seemed to work great in snow/rain/fog conditions. only problem with them is that the local yokels told me they were illegal. i have seen some HID lites (bmw) that should be declared illegal since they blind the living crap out of ya.
bottom line is that everyone has their own preferences, what works and what doesnt.