Just saw that they also made a TT version (LF3) for the 2014+ Cadillac CTS/XTS Vsport rated up to 420hp/430tq. Don't know what kind of internal changes the made, but seems like they trust it to go at least that far from the factory.
GM 3.6 Liter Twin Turbo V6 LF3 Engine Info, Power, Specs, Wiki | GM Authority

The GNX guys would probably get ticked about this quote, "The LF3 is the most powerful V6 ever from General Motors."