I live just south of St. Louis, Missouri.   I have seen on this forum about climates that are predominately heating(which you want I high SHGC) and predominately cooling (which you then want Low SHGC).  My problem is that where I live it is about about 50/50.  In the summer the temps. will break a 100 degrees a week or so and in the winter we will break 0 degress for a week or so.

So the question is do you go with a high SGHC or Low SGHC or is there a good window that works well in both extremes???

The International Building Code has a chart which will direct you to the requirements of your zone.