Think of it this way... You get the 3.73s for the same price as you could've gotten the 4.10s. You're getting 1 mpg or so better gas mileage with those 3.73s, but your car doesn't pull as hard. Are you gonna be happy?
I had a set of 3.73s waiting to be installed (based on friends' thoughts, articles I read, etc.), and then I joined StangNet. I do not race my car at a track (yet), and hearing testimonials from other StangNet members who had 4.10s on DDs swayed me to the 4.10s. Not a day goes by that I regret it! If anything else, it makes me stay close to the speed limit, so now I don't have to worry about getting a ticket on the freeway.
In the end you have to do what you think is right, but if getting 4.10s was wrong, don't you think SOMEONE on this site would've said so by now?