CMG Infinity = very old, discontinued years ago, low powered and quite dim, about 1 lumen. Built like a tank.
CMG Infinity Ultra/Ultra-G: higher powered version of Infinity with modernized circuit (also adopted by last versions of Infinity). About 3 lumens. Ultra-G is still sought after because of its tough construction and unique appearance.
Gerber Infinity Ultra: redesigned version of CMG Ultra after Gerber acquired CMG, manufactured in China. There may be more than one version of this. Construction has cheaper-looking-appearance than the old CMG models and it has been less popular here on CPF. Uses a newer LED for about 5-6 lumens output.
Fenix E01: very recent AAA light using Nichia GS for about 5-6 lumens output at quite low power. 5-6 lumens is based on comparisons with other lights and calculating from the runtime and inferred power level. Fenix advertising materials say 10 lumens but that's advertising for you.
Anyway the E01 and Gerber Infinity should be about the same brightness. The Gerber uses more battery power due to its older and less efficient LED, but since it uses an AA cell rather than an AAA, more total energy is available and the Gerber runs longer than the Fenix. (Of course it's much bigger).
Basically you should decide this based on whether you want an AA or an AAA light.
Modding the Gerber with a GS led should be pretty easy, if that helps.