K2 and optics

So there has been all this discussion of the Cree-xre. But I am curious about the announcement of the K2 and it's update.

Since I have not used the K2 at all, can someone tell me how it compares to the Luxeon 1 and Luxeon 3?

Can the current K2 be a direct replacment for a Luxeon 3? Do I need a different reflector?

What other benefits or things might be usful to consider before changing a Quadsink or PTS2 using LUX3 to K2s?

I know the current K2 is not as efficient as some of the current Lux3 and Lux1 LEDs, but the added drive current support might have it's benefits?

I could see a M*G 2C with some of the new K2s, being a really nice WALL of light for those times you need really bright light and shock is an issue...