The stock piping is long as makes all sorts of turns and varies in size. The upgrade elimnates much of this and helps with pressure drop. I use the PVC pipes (upper pipes only) and they work fine. I also plan on upgrading my IC, so I decided that it was a waste of money until then.
Speaking from experience, I would stay away from the Defcon IC pipes. The fitment is a joke, and i you have to cut the pipes to make them fit. I agree that if you're going through the trouble of upgrading pipes, it's good measure to upgrade the IC as well. I personally run the AMS FMIC and the Defcon pipes. The AMS pipes that were designed with their intercooler are supposed to be a good fit. The only issue there is the backlog of kits to be made, and the wait. At the time I purchased the kit, the AMS pipes were 3 months backordered and was forced to go the Defcon route. I wish now I had waited for the AMS pipes.
I can only speak from experience, and can't say much for the other kits.