It should be a noticeable difference going from 1500 to 0. Just berserk and prove bolts are the same.
I already tried that before, hence why I said I haven't felt the difference even with 1500 int as reference.
"Feels" aren't enough to prove something however and I don't have the time today to record myself casting bolts. Even if I did I assume the method Rydian is using to measure cast time is more accurate than what I would do.