I was just wondering.

i have a 2001 GSR, with CAI/IM/H/E, And i was just wondering whats the next best thing for my ride. I was thinking i could finish the bolt ons, u know a throttle body or high flow cat. But i was really looking for something where i'll will be able to feel a difference. I'm looking at the price range of around 200 to 300, 300 being the max though. if u guys are thinking internals, give some suggestios about long term or short what will it do to my car?

thanks