From my own experience, an i7 can run 100 tracks, but the real question is; do you really need a laptop? A desktop machine will give way better performance over a laptop for the same investment. And I agree that an i9 should outperform an i7, but that's not the only detail that matters. Speed matters more than the number of cores. In any case, get the best you can afford because that tends to give you longer service
