I have an 04' ZX-6R and i was thinking about getting a full Hindle exhaust...

I was just wondering how much of a power differenceam i expected to feel...

 

You should get at least 5-6+ HP extra and with the Full exhaust, a Power Commander anda lot of it will be at the top-end. You may lose a little torque at the bottom end but if you re-gear your bike like other members here have, you'll like it.