pg62, it's strange the way the human visual system works. We usually associate "whiter" with a higher proportion of blue wavelengths in the light projected by your headlights, or on other items (light sources, or items taking ambient light and displaying that light by luminance or radiance). You see all that foreground lighting with more blue in it, and the first reaction is "Wow, that's brighter, and I'm seeing more." No, it's not brighter, and no, you're not seeing more (especially in the distance), but it's the way our mere human being visual system is wired.
As a strange aside, many years ago (like the early 1900's) when white clothing would turn dingy after much use, stores sold liquid bluing which was essentially very fine iron powder suspended in a pH-adjusted aqueous solution which turned out to be blue. Adding this to the wash water made those dingy white clothes look whiter.
If you're getting brighter light now, your new bulbs are doing their job to contribute to safer night driving. If you're looking for so-called "whiter" light just for the effect, more blue wavelengths at the expense of useful wavelengths is the answer. My TRS D2S HID capsules have pretty much shifted to a bluer color temperature, possibly well over 5000k, after 4 years of use. I see less down the road than I did when they were brand new and in the lower part of the color temperature regime (4300k out-of-the-box), so I'll be replacing them soon.
As well, light output can diminish with years of use with any HID capsule; those with fewer metallic salts deposited in the HID capsule to support the arc discharge will tend to do this quicker (and have a briefer lifetime) than those from name brands like Philips, OSRAM, or even GE.
If you go HID, get a decent projector system. Knowing what I know now, if you can do something simple like bake apart the headlight housings, but do not wish to perform surgery and careful alignment of an OE-style projector (like, say an Acura TL type for example), then a Mini-H1 projector is your best option. They have a better light throw than the Mini-D2S I retro'd into my van, and the Mini-H1 bulb architecture is popular (continued support).
Food for thought.
OF