The $5k number came from me; it's a number I plucked out of the air for the additional cost not only for the the 8-speed, but the 6.2L SC, and all the other little things people want to add in make the SRT8s "competitive".
You can't have your cake and eat it too people. I'd love for the SRT8s to be 550HP with the 8-speed, massaging seats, ceramic brakes, etc. But the major advantage over all it's competition - price - is out the window.
If you think you're going to get a direct numbers-to-numbers (horsepower, 'Ring times, etc.) competitor for the E63 and M5 at the current SRT8s price point... think again.
If you add a blower, and all that torque, then you don't need more gears
But if Chrysler added 125HP to the 6.4 and cleaned up the handling so it rivaled the CTS-V/M5 set I would bet you my paycheck they would find a lot of buyers for the car at $55K
2006 SRT8 228,000 miles+ (ordered with F1s and options)
2015 Dodge Charger SRT Hellcat
650 pound feet of torque