When Roush called us up and asked if we’d like to review the 2013 Stage 3 Mustang the answer was an obvious yes. Our affirmative reply may not be for the reason you might think, though. Yes, a part of us simply wanted to hoon around in a 565 horsepower supercharged Mustang for a week, but another part of us – perhaps the more sensible part – was genuinely curious to know how the company had evolved its flagship model for this year. After all, the market for the turn-key …