I'm interested to know why you think it isn't windproof? I'm not discounting your experience, just curious. As most w/b membranes are completely windproof due to the fact that they have to be because of their waterproofness, I'm not sure how eVENT isn't completely windproof as well.
Air permeability, that which gives fleece and softshells a one-up on hardshells in terms of ventilation, is recorded through cfm measurements. The only air permeable w/b membrane that I know of is Schoeller's WB-400 which records 3 cfm (cubic ft per minute), helping it's breathability. This laminate, after it is applied, expands slightly resembling very fine foam. This 'foaming' action gives it it's air permeability. It is only used with 4-way stretch woven, or softshell, materials. All other membranes and laminates are completely windproof, or, in other words, record 0 cfm.
That's not exactly true. As already metnioned before, membranes like eVENT and windstopper have an open pore structure which allow a tiny amount of air to pass through. These amounts aren't certainly in the same league as true soft shell fabrics like WB-400, Powershield or stretch wovens which have CFM ratings from 3 up to 40 or 50. If I remember correctly, the CFM ratings for windstopper and eVENT lies between 0,3 and 1 CFM. Not much but enough to have an effect on breathability (it is the reason why eVENT performs that well) and why you can feel a slight breeze through the fabrics. Why do people say this about eVENT and not about windstopper ? It could be because windstopper garments in general seem to use heavier face fabrics and linings which have an effect too.