Nitpicky, but the New 3DS isnt more than 8 times faster than the Old 3DS: it has a quad core 800MHz processor instead of a dual core 268MHz processor. Even with perfectly scaled multi-threaded code, thats only a ~6x increase.
No idea how that happened, I guess I simply forget the dualcore cpu on the original model. But to one-up the nitpicky-ness one could argue that the "real" game performance still has a more than 8x increase, since both models seem to reserve one core for the OS.