I'm a little late, but maybe I can still chime in on the V6 Mustang versus a Bonneville. I have a naturally aspirated Series 2 99 SLE, aka the SLO. It has just the mods you see at the bottom. A friend of mine had a V6 Mustang with a manual, and we did a ton of work on it with long tube headers, a fender well intake, porting & port-matching the intake manifolds, throttle body, colder plugs, days of tuning, all that, and then we raced. He drove my Bonneville, and I drove the Mustang. I was completely blown away by my own car - he put several car lengths on his Mustang already by 40mph. That'* nuts!
Another time he was driving my car, and I drove his to scan it for whatever may come up. I went wide open throttle, and after about a second I saw my Bonneville just zoom right past me. I pulled up to him at a stoplight and asked why he was racing. He said he wasn't, it was just half-throttle, and he only wanted to get away from how loud the Mustang was. The Bonneville back then had a stock exhaust, all leather, four doors, an automatic, everything working with twice the mileage (86K on the Mustang), and it just trashed that Ford. And the SSEi is even faster!
I see on the previous page that you posted you bought the Bonneville. I'm just letting you know this so you can feel even better about your purchase. Do mods!
94 STEi and 99 SLO