I posted the original quoted info by NC_VX, I didn't test the 18w bulbs because everyone was talking about how previously tried larger watt bulbs were starting to melt the housings. I figured 12w was gonna be good enough and it was, they look great. Match my Piaa P-3000 perfectly and I'm very happy.
I'm not sure your gonna get much more light out of them, but if you do try the higher wattage let us know if they cause any problems.
Keep in mind the parking lights dont really put alot of light to the ground, they do put some, but not alot. They are more for people to be able to see you or those cases where your checking distance between you and a object in front of you. The 12w bulbs work perfectly for this. (ie: they are not fogs, if you want those try checking moncha's hella micro fog replacment) You wont have to worry about the lense melting or deforming and you'll get your really high 50w fogs.
Dallas4u, did you ever get to compare the two different silverstar brands? If so, what was the result? Were the osram's any brighter? I know I looked at both online and was thinking about the osram's for their additional brightness, but it just happend that I was in the auto parts store and they had a great buy 1 get 1 at 50% off sale going that saved me about $15.00 so I stuck with the silvania version.