Wow, Vicomptel, a name i haven't heard in a while (dealer who got out of the flashlight biz a while back, I think). CMG is long since shut down (absorbed into gerber). I'd call Gerber on the phone and discuss the situation:
http://www.gerbergear.com/contact.php
When you say "ultra version" you have to understand there are TWO ultra versions that are relevant here: the CMG version (that was also, confusingly, sold under the Gerber label for a short while):
http://www.flashlightreviews.com/reviews/cmg_infinity_ultra.htm
and the current, all-Gerber version which is a completely new design:
http://www.flashlightreviews.com/reviews/gerber_infinityultra.htm
The CMG version is basically a slightly updated revision of your Infinity, with the power level cranked up so that it's about 2x as bright as before, though the battery won't last as long. The metal parts are just about exactly the same (the very oldest Infinities, of which you might have one, had a matte finish that was less durable). It was discontinued a couple years ago though you can occasionally find them if you keep your eyes open.
The new Gerber version is a completely different design where you twist the tail rather than the head to turn the light on. It does not feel as solid as the old version (stamped rather than machined, etc). Conventional wisdom here on CPF is that Gerber messed up a good thing (the new version must cost less to manufacture) and the new version is less durable. Separately from durability though, it will be brighter than any of the CMG versions just because it uses newer LED technology. The old version is sought after and the new version is not very popular. Beam patterns will be about the same for all three of these lights.
So, the concern that people are expressing is that if you send your old Infinity to Gerber, you might end up with the redesigned Ultra which is less of a classic light.