We are kidding ourselves if we think that SFI is accurate when engine speeds are high. 6000rpm has 1 cylinder's intake valve opening on every other rotation of the crank or 50 times per second. I'd bet the farm that there is some injector duty cycling overlap independent of intake valve position. I have heard the rumour too. I didn't know if it was an actual change in fueling strategy or simple lack of time to perform sufficient injection in the time allowance. DI is a completely different animal. Its injection occurs during different positions of the piston, no matter where the valve is, very precise.