Don't live off your temp gauge and think everything is okay...you don't want your fans running non stop to solve a problem. They work in sync with the cooling system for a reason.
Ford didn't waste + amounts of money to design a radiator because it would be FINE. Trust me auto companies don't waste money unless its needed.
The increased compression along with aggressive timing (93 octane) created a hotter combustion. Resulting in ford needing to add extra coolant to the equation for long term drive ability.:idea:Sure the 3L's are not as equally comparable (compression, tunning etc etc) but the added displacement still creates a considerable amount of combustion.
So try to find a svt radiator if you can. If not pick up a v6 radiator for the time being.