Well.... The Tec40 is what I would call "the poor man's E2". About the same output as the E2, but a lot less cost. Get the textured reflector - it should come with it already, but some are packaged with the smooth reflector.
The Impact runs a single nichia white LED in a deep reflector behind a convex lens, creating a relatively tight LED beam. If you prefer a longer range beam as opposed to a flood of light from an LED flashlight, the Impact is a good choice. In an unscientific comparison I did this morning, I could make out the same detail at the same distance using the Impact or a Tektite Expedition 300 (7 LEDs). The 300 gave a larger flood of light while the Impact created a distinct "spot" of light, illuminating a smaller area, but effectively having the same throw despite using only one LED.
As a bonus, the bodies of the 40 and Impact are interchangable. Also, PT makes an Impact 2 - runs on AAA instead of AA and output is almost identical (less than a 10% difference in initial output between the two). Check out Pocketlights.com - they have them.