I was brought up to be a mopar guy as well, but not being able to afford a decent one in high school brought me to mustang.
Both are mean cars. The GT500 has more hp's and torque (540 and 510). The Roush is rated at 435 and 400. Many see the Roush's being overpriced and underpowered for what you get. I guess it's up to you. I'd do some research, they're always changing/uprgading those two particular cars. For example, the 427's intercooler is twice as big and more efficient as the 08/09.
I personally would take the GT500. I've always liked them. But then you could always buy an 03/04 termi cobra and spend half as much on the car itself, and spend the other half to make it outperform the other two.
12 Black GT500 SVT PP l 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.