With Shure black olive foamies the SA6's actually isolate better than the E500's, probably because they insert a bit deeper.
I've made a few posts with some impressions/comparisons of two from back when I had both so you if you want more detail you might try searching using my username. Briefly though the SA6's have a bit leaner, punchier sound with better extension on the top. The E500's capture decay better whereas the SA6's are better at portraying the initial transient. The E500's have a soundstage that's set further back and wider but the SA6's is deeper and has more height. I personally really like both but for different reasons. The SA6's customizable sound, modular, versatile design and cheaper price gives it the edge in books.