event is only different from goretex in that they don't coat the inside of the goretex with a oil repellent layer. the waterproof breathable ePTFE layer can be clogged by dirt and oils, so gore protects that layer with another layer, which hampers its breathabillity a little bit. event gets around this by making the ePTFE layer itself oleophobic. how that is done is a trade secret. this essentially removes one layer that affects the breathabillity.
from an industry site
A few years ago, the U.S. Army’s Soldier System Center in Natick, Mass., performed breathability tests on some common outdoor fabrics. Leading the pack of tested materials was the eVent laminate which, depending on relative humidity, was between 1.3 and 3 times more breathable than the next best material, Gore-Tex XCR. Following this, the results clustered together, with the best-performing materials approximately twice as breathable as the least. In descending order of breathability, the results were: Gore-Tex XCR, Gore-Tex (standard), HydroSeal (The North Face), Membrain (Marmot), Sympatex, Conduit (Mountain Hardwear), and OmniTech (Columbia).