I have both of em sitting outside and I know that the 5.0 is faster and more fun to drive. But the Mach 1 is a brute forced car. It muscles its way around. The 5.0 is just easy going fast. I personally am getting tired of plain ol 5.0s at the track getting there asses kicked. But I love to see the old ones run down a new camaro and look like nothing fancy. As a matter of fact one of the guys thats in our suite at HRP has a 9 sec 65' thats just plain awesome. Dont get me wrong on the 5.0s. Its amazing how fast they go but too many people seem to own them now. I guess its because I was loving stangs when they were'nt cool and now everyones got a stock stang and someone told them it would run down anything on the road. Then they talk a bunch of trash and go out and get killed on the track. Its embarassing sometimes. But I still hold my head up high with my FORD RACING hat on.
I really just comes down to what you prefer. Or you could just toss a coin.
Either way, good luck!