2003 Anniversary vert. I've tried everything I can think of to be able to "SEE IN THE DARK" First tried all the "great" new 9006 halogen bulbs. Ultra's ,Super's, Blue tip, gold tip 4500K, 6000K, NOTHING worked. Then went to HID's with ballasts that burned out every 3 months. Then modified 9005 high beam bulbs to fit into the low beam housings, but because of their clear tips, I was blinding oncoming traffic even when I aimed them low. Finally I saw on E-bay a combo halo, projector / high beam sealed unit, not too expensive, figured, what the heck. Curiously it came with a harness to allow both bulbs to come on at the same time....DON'T WANT THAT. Next, I didn't connect the "halo" cause unless the headlights are "up", nobody see em' I just wanted something to increase the low beam down the road. They come with an H11 low beam bulb installed and you use your own high beam bulb, ( in my case an HIR 9011, clear tip, modified by trimming a 1/8 inch piece off the plastic tab....fits perfectly. NOW....the H11 low beams are terrible, they look yellow and are worse than the stock junk, ( Thanx GM ) MY bottom line question is, I know some guy's with other vehicles, not ours, have adapted H-9 bulbs, 65 watt into sockets that take H-11"s 55 watt ...Will there be any negligible heat difference in the wiring? Thank you for any help.

If you're willing to spend another $700, in my C5 I had the T84 Euro-spec headlight housings with PIAA Xtreme White H4 bulbs and they were MUCH better than stock.

To answer your original question...

If you're going to buy new bulbs, I'd just get a quality H11 bulb (like PIAA) instead of trying to modify a different size.

The stock wiring can handle the 65w bulbs, but it may not do it forever without a high wattage harness (relay) installed.

Thank you for the input. The car is a daily driver so it NEEDS to have good lighting. At this juncture, I'm between HID's again, with better ballasts that don't burn out.( Bad feeling when I start the car and only one headlight works).Or reinstalling the stock set up. Biggest problem is the reflector in the headlight housing itself. Would love to see an after market unit that has a shield or cut off so at least I could have lighting as good as a COROLLA,@#^$@#^. I'll look into your suggestion of the $700 option. Thanks for your help.

Well I finally bit the bullet and ordered a set of projector / high beam lights from (don't know if I can mention his name on here, but his company has the same name a a popular little red wagon ). $650, took a month and a half to get them, but the lighting is absolutely AMAZING. Anyone with a C-5 that has tried everything as I have to see at night.....YOU MUST BUY THIS SET UP.
It only takes about 2 hours from removal to install, looks great and you will NOT BE DISAPPOINTED. I was parked next to a C-7 Saturday night and the guy was so impressed he's ordering a set for his "99. The unit comes with a small harness that allows you to have both low and high beams on at the same time. The "cut off" looks like I'm driving a brand new car.
Next project is to remove the stock JUNK "fog lights", which also have had all types of different bulbs, HID's etc, and replace the entire set up with a PIAA or HELLA style Driving Light....Finally truly satisfied with this car!!

Hello bobert
I am interested in your change of projectors, could you give me the coordinates of the site selling this set of projectors.
thank you in advance

2003, euro version. Bulbs are H4. Installed Osram Night Breakers, the visibility is way better.