I replied on the WERA board..but the stock system is uber hot and no good way around it.
You cant bypass the cats on this system vs the 06's. The cats are made into the lower header section so you will have to gut it at the very least.
I have the same set up for the most part and its ok on heating, but the endurance race melted my plastics. also you will have to trim down the plastic up front a few inches. I posted pics on the wera board on a Hotboies thread. I will try and look it up.
Id say gut the cats that are in the header, trim the front of the body work down some and double wrap the pipes.
You can see how much I cut down in this picture. The original body work meets up right under the radiator. The stock headers bow forward and put it too close to the body work while the after market headers are straighter downward away from the bodywork.
I still fun stock exhaust, gutted cats in the air box, boom box cats removed and M4 slip on. For trackdays and race sprints its fine, but 6 hour endurance fried everything.