If you have an older L1, it has a low dome emitter in it. The beam that you are getting with the NX05 optic is about as good as it's going to get, unless you swap the emitter too. If you have access to a heat gun or toaster oven, and a vice with protected jaws you could do the mod yourself. If I remember correctly, I started doing these sorts of mods with a butane soldering iron that I got from radio shack. Once you drop the high dome luxeon into it, you would have a couple of options with regard to the collimator. If you want a concentrated beam similar to that of the latest KL1s, you could go with a Fraen Low Profile optic. Just keep in mind that this will give you nothing but a concentrated beam with no sidespill. Alternatively, you could drop an IMS 17mm reflector into it for a more conventional beam pattern that still has good throw, but also offers a very nice and useful sidespill.
When choosing an emitter for your L1, I'd just keep in mind that the L1 runs the emitter at about 350mA, so I'd look for either a TWO binned Lux III or a nice 1W luxeon.
Running at 350mA, I wouldn't be too concerned about whether you get a 1W or a Lux III. Just try to get one that will produce a nice tint at 350mA.
If you do the above, you're gonna like the light again.