well, you guy's also have to take into account the fact that its a factory produced car. look at the nissan skyline GTR. a finely tuned 2.6L twin turbo I6 only making 276hp. thats because japan had a 280hp limit on all factory produced cars at the time it was built. so what they did was put in a finely tuned motor and add an extremely restrictive intake and exhaust system and dropped the boost down very low. thats why GTR's are known to produce upwards of 400hp with just the addition of intake, exhaust, and a boost controller.
its basically the same concept with the SRT-4. they want their car to be affordable, so they cant give it so much power from the factory. i guarante if you get rid of the restrictive manifold, turbo, and downpipe combo, add 2.5" downpipe, better intake and exhaust, a better manifold and turbo, and up the boost to 20psi, you'd be getting around 280-300whp. but you wont keep traction very easily without that LSD. i mean, its a little more money than just intake, exhaust, and a boost controller, but i think the power would be worth it.