Hi Jim,
A few years ago I fitted some 70w aftermarket HID's to my old IPF 900 spots. They were 6000k, and tended to be a bit blue-ish.
I found they were very focussed, giving a real pencil beam, but there was so much light that there was still plenty of illumination to the sides.
I've since changed them to 4300k, and fitted some spread beam lenses. I find 4300k gives better coverage, or better light.
The light seems to be somehow "fuller" or "thicker"
. Not yellow-ish, just less blue-ish.
The beam is now a flat-oval shape, with a better spread. The colour temp is easier on the eyes, but there is still plenty of reflection from signs.
I notice a slight buzz from the ballasts, but only when standing next to them. I also get some radio interference, but it's not an issue for me.