I'd assume the E-Flex frame itself is as comfortable as E-Vents, and i've had E-Vents before, which were comfy except for the weight (and not as breathable). Combined with the Flex bottoms, i'd rate the E-Flex & Proflex identical in the comfort dept.
I own both the Proflexes and the E-Flexes. The Foam is the same and really is what makes the mask the most comfortable. I can breathe better in the Proflexes but I like the quick change lens and ear pads on the E-Flex. I find myself sticking my Proflex bottoms on the E-Flex now every time I play. Best of both worlds.