Wow did I reopen a can of worms. The only intelligent comment since I posted was by meat_WRX. Yes heads w/ cams can improve the overall powerband but the fact remains that the stock turbo will fall on its face at higher rpm. So, unless a turbo upgrade is in the near future all these gains will be minimal and not cost effective. You will spend 5k+ for maybe 50whp and trq (being optimistic). That doesn't include the cost of the parts and labor involved in upgrading heads.
As you can see it adds up fast. Just an upgraded stock location, fuel system, and tune will cost ~3k and can get gains get better gains.
My .02