Do you have projectors retrofitted into your headlights? (I thought the 05 STi had halogen headlights? Maybe I'm wrong.)
OEM is usually ~4300k for almost every car manufacturer because that provides the most light output.
Don't drop in HID bulbs into halogen reflectors/projectors. It's provides horrible lighting, the light scatters, and it's dangerous for you and everyone else on the road.