Roughly 10% increase on direct CPU comparisons (i5 to i5, i7 to i7), which is nice but not noticeable to most people. However moving from an i5 to an i7 will have an significance performance difference if the software you're using can take advantage of multi threading. Look in to your music software and see if it takes advantage of multithreading or not.
If you were building from scratch, I'd say go Skylake as the costs are roughly the same as building a new Haswell system. However since you're only wanting to move to an i7, I dont know if playing an extra $200-$300 would be worth it to you. You might be better off putting that money in to a better video card for gaming or increase in Memory and SSD's for the music editing.