I believe the PIAA XtremeWhite H3 is a 4150K color temperature and your 9007's are a 4000K temp. I'm actually surprised you find them to be significantly more yellow than the H3's. I have a set of 9007 XtremeWhites that I ran for awhile in my 2000 and found them to be rather white actually. Anyhoo, OEM HID's run around 4300K color temp and AFAIK there are no non HID bulbs that match that unless they are illegal and innefficient. To acheive that color temperature a regular bulb has to be coated and that reduces it's light output. You would be buying them more for color than performace. IMO, if you're going illegal anyway you may as well get real HID's, but I'm not sure what the results would be in the '02 and '03 light housings. They tend to direct an awful lot of light at oncoming drivers so putting in HID's may be asking for the wrong kind of attention. Truthfully, of all the regular bulbs I've sued I found the PIAA XtremeWhites to be the best because they are close in color temp to HID and also put out quite a bit of light. I honestly don't think you're going to find a better bulb than that in a 9007, but I could be wrong.
I ended up installing real 4300K HID's in my 2000 Xterra but I also upgraded my lamp housings to some with better reflectors that have a sharper upper cutoff than the original lights. Let me tell you, the light output is amazing!
Something else you could try that may or may not help would be to upgrade your wiring harness. The better wiring could possibly give more power to the lights and make them brighter since you are running larger wire directly from the battery, but I can't guarranty it. An upgrade harness runs about $50. You will want the upgrade harness anyway if you decide to go to HID's.
