Top end is all about breathing. The easier the air gets into the combustion chambers, and the quicker it gets out, will help your top end. The trick is to do things equally. For example, if you threw on a set of 3.5" pipes, you would lose top end because there was no longer any backpressure. An H pipe would be an excellent place to start, and I always support anyones decision to go for cold air.
Take care,
-Chris