Power is in the head, ported head will really open it up. Make sure someone with lots of experience porting heads, and is very good does it, (dont cheap out) so choose wisely, cuz a bad port job will do the opposite obviously.
This will be my next mod on my 06. But its not cheap. You could also do a big bore kit, the 04/05,s have a good platform for big power.
Keep in mind the bigger the bore the more stress on the cylinder. Me personally i stick with stock bore. But you can do a 470 ish bore kit and keep longevity on the cylinder.
But the head is where its at my friend.