Before I smashed them into millions of tiny pieces and spread them along about 100 or so yards of the M6 I had OEM facelift xenons on my A3; and obviously they're just the same, dipped is xenon, high-beam is halogen.
I'd always thought of having a bi-xenon setup, but having decided not to bother and go the OEM route I was by no means disappointed. I think I'm right in saying that yes, the reason the hi-beam appears brighter, and casts its light over a wider area is down to the reflector / lens and the bulb has very little to do with it.
I think it's also probably fair to say that a bi-xenon setup may produce a brighter light overall (potentially giving a greater overall distance with 'usable' light); but I'm not sure how much you actually need it. I noticed that (comparing to my pre-facelift halogens) the dipped beam was noticably brighter, offered a larger area of usable light, and offered a cleaner (closer to natural) light. Someone also used the word sharp to describe their output which I thought was pretty apt. The high-beam were also a massive improvement, and to be honest the few times I actually needed them they were certainly sufficient - I really don't think I'd have needed any extra or different output a bi-xenon setup might offer. A while after I fitted them, I put some Philips Power2Night GT150 (or something like that) bulbs in for high-beam and they offered a bit of an improvement again - probably nothing like another HID lamp but they were better than whatever started in the clusters - certainly a bit brigher (perhaps not the quoted 50% but certainly over 10 at a guess), and indeed a slightly lighter colour temperature. That only reassured me more that bi-xenon would probably be overkill. Of course some may disagree, but I was pretty confident.
In terms of temperature of the xenons, the OEM are 4300/4600k (I can't remember which) and to be honest, you could tell they were xenon, but subtly might be a fair description of how that came across - you obviously could tell when you first lit them from cold and they take a second or so to warm up, and then every now and then you'd catch a little flash of gleaming white / really light blue. 6000k are more towards the late-model Merc / BMW type appearance that seem a bit more blue a bit more of the time. 8000k is another step up (and a bit of a drop in luminance), probably more blue than most people would like - but having said that there are kits by BOSCH HID (
http://www.boschhid.com/en/index.asp) at 8000k which I've thought about purely because half of me wants to believe BOSCH HID is actually a proper BOSCH (as in, Robert Bosch) brand and not a touch of far-east trademark borrowing (I'm only thinking about a HID kit because I doubt I'll get any more OEM xenons at such a steal for the next car so facelift projectors and a HID kit it will have to be for a while).
Sorry to have waffled on, looking at that little essay I think I might be starting to miss my xenons and the motor they sat in a bit! Doh!
Anyway, hope it's some way helpful,
Regards,
Rob.
EDIT: Small pic, but my OEM xenons are the ones on the right in my avatar... It's probably a fair pic because that's what I'd say is an average of how they looked, at some angles (and ambient light conditions) you might catch a flash of some other tones though.