If I'm reading this right you seem a bit disappointed and expected more.
You're in the ball park with your peak numbers. That equates to 542 hp at the crank. Vortechs with canned tunes on stock innards should be around 550 hp give or take 10 to 20 hp depending on conditions and the type of dyno. If it was a hot, muggy day your numbers will suffer. Low pressure fronts moving through the area will affect engine output. Even the tension on the straps holding your car on the dyno can make a difference. Results can vary from one dyno manufacturer to another. Remember, dynos are diagnostic tools for tuning purposes. You use them to see if changes to the engine improve or hinder performance. Also, more important than a peak number is the power curve. Your tuner might have tuned for a better torque curve which might mean a lower peak number but better overall performance. I don't have enough information to know. You might want to talk to your tuner to see how he set your tune up.
You also didn't say which Vortech package you have. Is it a V3? Intercooler? Injectors? My Vortech runs at 8 psi as set up by the factory.
A tuned catback might give you a bit more performance than the resonator deletes. But, will it be significant? I don't know. You'd have to get a lot more ridiculous with your bottom end before the cost and hassle of long tube headers will be worth it. The stock SRT manifolds flow pretty well.
Instead of trying for more horsepower I suggest you work on applying the power you have to the pavement. Suspension and tires will make a huge difference. Strut braces and Hotchkis totally changed the driving experience in my car. I'm running Nitto NT05s which so far are the best street tire I've ever used to handle the extra boost as well as the improved cornering from the suspension upgrades.
Gotcha. You're definitely right there with the rest of us especially if you're only running 6.5 psi. A little cooler day, less humidity with higher barometric pressure and you might pick up quite a bit more rwhp. Your torque curve looks nice and flat from 3,000 rpms on up. You're well over 350 ft. lbs under boost right on up to redline. That to me is the more important number than peak hp.