Another thing that i you need to pay attention to is the resonance, these cutters can give off a "screaming sound" this is bad as what you are hearing is the cutter resonating. this will almost definitely cause the cutter to fail. Id experiment like you say keep you feed the same 2.5M/M and reduce or increase you RPM until the screaming goes, you should hear a nice cutting sound, I if get 5 mins ill do a vid for you.