OP, the reason stock vehicles use 4300K is because it provides the most actual light oputput in terms of "lumens"... I put 5000k in my wife's factory non HID headlights and she loves them (and she's not into car modding)
I repalced my factory 4300K H ID's with aftermarket 5000K HID's... and indeed light output is slightly less than the factory 4300K, but not very noticeable...
regarding putting them into the non HID headlights, for our cars, it won;t be a problem... the reason the civics and older 90's based cars are blinding folks is because of how the headlights were designed. nowadays, even factory headlights have a pretty decent beam cutoff pattern, so adding HID's doesn't really cause glare the way the 90's designed headlights did...
Blackmobile wrote:you won't get a proper stock look with aftermarket hid's. not unless you do a retrofit and rip open the headlights. the fact is that a non-oem headlight uses a reflector bowl, so when you put in an aftermarket kit, it's also using the same technology. so you will get a bit of a "flood" of light, but as long as you aim them properly it shouldn't be an issue with blinding oncomming traffic, most of our cars haven't needed to be aimed.
most of this is INACCURATE! Both the factory HID and non HID headlights use "reflector bowls" to reflect light for the headlight. The only vehicles that don't use these are vehicles with "projectors"
the difference in the Altimas that come with HID vs the ones without (in addition to the ballast and bulb) is the orientation of the reflectors inside the headlight. The HID headlams have a different vertical reflective surface which suts down a glare a bit more, compared to the non HID headlamps. this isn't really discernabl;e to the avaerage person until you look at both of them very closesly (I have)...
so again, tehy both use reflective bowls, they both have better than average cutoff lines, so you won't blind folks if you put in an HID kit in your altima...
what color you ue is entirely up to you... I agree with what the companies have been telling you OP, I would go with 5000K as it puts out pure white light, and although it puts out a bit less lumens than 4300K, the look is much, much better than 4300K... once you start with 6000K and above, you REALLY start putting oput A LOT less light compared to both 4300K and 5000K, and the blue look looks a bit rice to me, but some folks love it... just look at some photos of various colors and go with those, but my suggestion would be 5000K