The TerraLUX MiniStar5 SSC seems like it'll put some life into your 5D Mag. It's the newest LED replacement from TerraLUX and uses the latest LED technology. It'll run on 3-6 C or D cells, constant-brightness output for up to a claimed 20 hours before starting to dim, and plenty bright.
By the way, I have a couple lights with SMJLED's, too. I have a 94 cent Walmart 2AA light and a Garrity 2D. In the 2AA, it makes a remarkably good around-the-house flashlight. The 2D is a good complement to the 2AA because the 2AA is great for short to medium-range use, and the smaller, more concentrated beam of the 2D is better for long-range use.
Some flashlights will perform poorly with the SMJLED because of the way they're designed. The beam just looks crappy. So, if anyone decides to try the SMJLED and the beam looks awful or disappointingly dim and diffuse, you should consider trying it in a different kind of flashlight before giving up on it.