Fastburn

Just curious, I've seen several great guides, but they all seem to revolve around I4. Most of them recommend you six slotting something, then filling 5 if not all 6 with the same enhancements. Since I6 came out, anything over 3 slots of the same enhancement is said to be a waste. Sooo, how accurate is that? Is 4 or more same-slotting obsolete?

Thanks for any help to come this way.