John,
You've pretty much summed it up. Ratings typically go like this, lowest to highest:
E-Glass > S-Glass > Graphite
E-Glass is the standard (common) fiberglass reinforcement material. S-Glass looks and handles exactly the same but is made from a higher-strength fiber which gives about 40% higher tensile strength, 20% higher modulus, and greater abrasion resistance. No downsides or negatives that I'm aware of other than not as common to find and higher cost, as you've already found out. Numbers I've seen suggest you can make the same rod out of ~30% less material by using S-Glass, making for a lighter weight rod, also.
Here are a couple links to a more detailed description and comparison:
Fiberglass types
Fabric Information
