Still have my 2005 STX 4.2. It's been great to me. 256K on it's original engine and transmission. I got it with 86K, and it has never given me any trouble.
The Mustang is also a great one. Since I seem to steer towards the 6'ers, I bought a 2011 with the 3.7. I've installed a turbo on it, and it's fun to pull up next to the 5.0's and give it a whirl!
I totally respect the V8's; there's no replacement for displacement. If/when I can afford a Boss, I plan to purchase a clean used one. Since I like to track the Mustang once or twice a month, the Boss is what I'd love to get my hands on. With a little work, the 3.7 can be made to run up there with the big boys. However, with the same budget, I know I could make a killer 5.0.
it just takes money. Time I have plenty of.