To start off with i've never heard of "Syntha-6", but protein is protein, i use regular ole' Optimum Nutrition Whey. Your not gonna see a difference in proteins, like switching from a protein powder to another, it's not like "wow, i'm so much bigger now that i've been using this protein powder", it's JUST protein. Your not gonna see that much of a difference.
EDIT: K, just looked it up...45 dollars BISH!?!?!? Heeeeeelllllllllllll naw. I get mine for 25 dollars, and i bet it's just as good if not better.