The silver plate you are talking about is a casper shield(I guess you have an H4-2 kit in your alto). What this shield does is block some of the light when the bulb is in the low beam position(a little inside) to simulate a low beam.
The chrome reflectors of the headlight surrounding the bulb negate the effect of the casper because the bulb has a different focal length to that of a halogen bulb for which the reflector for designed for originally.
So whether its a 3000K bulb or a 10000k bulb, it does not matter as it's not designed to be used in a halogen reflector.
BTW, the reason why the 10000k bulb irritates more is because it more blue and blue is a color that irritates the eye even though the 4300K throws WAY more amount of light than the 10000K bulb.
Put a 4300K bulb side by side with a blue-er bulb like 8000/10000k the blue bulb will seem brighter even though in reality the 4300K bulb is way brighter.