I just purchased Bikilas a couple of weeks ago (my first pair of VFF!) and I had a similar issue. The instep felt just a little too tight, so I tried one size larger in the Women's, but they were too big. I then tried on a pair of the Men's shoes in the comparable size as the original pair I tried on, and they fit perfectly! I am bummed that I don't have a pair of snazzy pink and orange Bikilas, but the blue and grey ones are almost as nice
Good for you, it is not always as easy to find such a perfect fit.
You should try them on, the ones in the store, and compare them both. If the ones you bought are toooooo big, maybe you could even bargain an exchange at the local store.
the moc or performa has the thinnest of them all, and is not designed to be used outdoors, is like using a leather glove on the feet, there is much ground feel; but not much resistance.