I know the X1 is in its fourth generation with a better emmiter and reflector. Much better than the last version. I think there is a thread around here about it if it wasn't lost during the crash. Still single stage though.
I have the new T1 and find it a vast improvement over its predecessor: bright, much better tint (the older version was yellow at near incandescent levels) and very handy two levels. The light is actually small enough to EDC.