The Up-pipe is a great mod and should be done. Don't use an MBC. The Up-pipe will as previously stated, allow your turbo to spool much quicker which will fatten up your TQ curve. Fattening up your TQ curve puts more power where you will use it most often in daily driving.. Try to get an Up-Pipe with the same diameter as the stocker, this will keep the air moving at the same velocity which will spin the turbo faster as well. A larger diameter Up-pipe will slow down the air negating the cat removal, not completely but none the less.. If your going to spend the money spend it right..
02 WRX.. "It's fun when it runs.. Problem is that it hardly ever does..."