I picked up a Gore Finish Line from Performance when they put it on sale. I should have paid closer attention to one of the posts made about the Gore stuff fitting tight across the chest. A medium works for me in just about any make of jersey or jacket. With Gore it was really tight and bunched up under the arms.
I returned it for a large, which I have been commuting and riding with over the last month. Now it doesn't fit ast tight across the chest, but the cut to the waist is not as aero as I would like. Overall, I am pleased enough to keep it. The pit zips definitely make the difference though. This Gore fabric does not breathe nearly as well as I would like, which several posters pointed out. So on anything but a short ride, my arms tend to get pretty damp. The pit zips help but only on regulating my torso temps. It definitely is good at wind blocking and keeping the damp out though, which made my rides in the wet last week a lot more bearable. I ended up having to be content with that, and wet arms. I'm glad that I got the jacket at a close-out, Performance Club member price.
A PI Barrier jacket by comparison has its wind blocking material up front but also is designed to vent to its rear. I find that moisture doesn't build up at all, unless I give it no choice by wearing too much to begin with. The cut is very aero and rest of its features are top notch. The fabric on it is more comfortable and moveable too. If it had pit zips, I would call it perfection.