Is yours an '11? It looks like all of their frames (now at least) either have a 73 or 76 degree seat tube angle (you can choose the angle on any size). I think on most bikes there isn't much difference in seat tube angle throughout the line.

When you're being fit to a bike your saddle to BB distance should be already set. Since the seat tube angles are all the same, the only difference between a smaller and larger frame (at least in terms of setback) would be how much seat post is sticking out of the frame. With a smaller frame you'd have more seat post sticking out, but that seat post would the same angle as the short seat tube. With a larger frame you'd have less seat post sticking out, but your saddle would end up in the same position. Your BB to saddle setback and height would be the same regardless of the frame. The only time a bigger frame wouldn't work is if you bottom out your seat post before reaching your proper seat height.

Whether you got a 56 or 58 your seat post would end in the same position, you'd be in the same place on the rails of the saddle either way. Now if there's much of difference in seat tube angle, it'd be a different story. I don't think the difference in the angles would be so great that you'd need to do much more than a slight shift fore/aft.

The only thing that matters (in respect to fit at least) in a geometry is Top Tube length, everything else can be adjusted (unless the frame prevents you from setting the seat low enough or high enough than a minimum insertion line on the tallest seat post available)