My findings...

The loadbalacing algorithm intelligence, the basics are fairly similar in function, though performance on the GSS was nowhere near the GTM. What separates GTM is the ability to combine in any fashion all the basic methods into one, plus a few more advanced ones, weighted by our preferences. Now, beyond the loadbalacing algorithms, the GTM communicates with the Big-IP in a way the GSS cannot, so it can gather more advanced availability and performance data with which to make a decision. Also, the GTM is better suited to provide name services beyond it's wideIP's, whereas the GSS was really only intended to be delegated to for those specific services that it will load balance

Francisco