About the only time we would see demand for cat 5 or cat 6 shielded was for harsh environment such as a manufacturing environment. Cat6a,  unlike the lesser performing catagory cable is frequently called out in  shielded variations as well as the unshielded versions. I recently read this white paper that does a really nice job on why you may want to consider shielded cat 6a. Click here for the white paper: Have you installed cat6a yet? if so let me know what your thoughts are.