Oh thank you I didn't know about VBA-M ! Thank you for letting me know.
If blargg is behind it, then it has to be great.
EDIT : Nope, the intro is still slower than on real hardware. My guess the CPU usage is close to 100% but slightly less, and that an error in VBA's CPU core makes the code take more cycles to executes, therefore making the game lag and missing occasional frames, so that the music ends before the intro actually finishes.