Just wait a few months and throw a badass Flowmaster kit in there. Delete the cats and run an off-road H-pipe. The difference in power and sound will be noticeable. I believe it's a 5% increase in power with a full catback kit, so it would add about 20HP.
You might not think the exhaust system could be improved upon, but it can. Granted, the stock headers are probably almost as efficient as pricey aftermarket ones, but an aftermarket catback system will have higher flowing mufflers and expel heat much easier without catalytic converters.
The only problem is that many states have annual inspections, and they do check it. My best recommendation would be moving out of the gestapo states that still force inspections.
