If you are looking at further improving your Tippmann M4's performance, the Tippmann owners group on facebook would be the best place to do it, not here unfortunately. (Not knocking the forum, its a great place!)
You should be looking to do the TDC mod (Top Dead Centre) to it, the hop up is the Tippmann's weakest component in the eyes of many. But hey, not bad for their first venture into the airsoft market.
Also, as someone has mentioned, it will perform better on HPA.
I hope you are enjoying your tippmann as much as I am!
