Q1. I'm not familiar with the X5 but if you previously had 2xCR123 primary cells in it then Surfire cells will work fine. I personally choose SF cells as my experience tells me they have a longer shelf life than other cells that are more easily available in the UK (Duracell, Everready).
Q2. In no real order my recommdations would be...
Photon....every keychain should have one
Arc AAA, lowish output and generally bluish in tint but built like a tank with very long runtimes
Fenix EO1 - very well thought of here
Orb RAW NS/Ti or Draco/Drake - very bright and the jury is equally split over which wins - you need to accept rechargeable only option though for all but the Orb Al RAW.
Endeavors Mako - TBD but looks wicked
PhotonFanatics Killer - any colour you like including black
and allows button or AAA battery choice
Surefire Titan - some carry on a key chain but it's a bit too large for this IMHO and you need to make sure you get a good one as this was a limited release and there was a disproportionate number of bad ones. A good one
is very good though.
Endeavor Aeon - as above apart from the fact that all that were released work perfectly (I think)
Have a look around:thumbsup:
Hods