First of all, back pressure is pretty much a myth. The less back pressure you have, typically the better. What you actually get from "more restrictive" exhaust is typically just higher flow, which can cause better scavenging, but you have to get it in the right way. If you are trying to flow X amount of CFM through a pipe and you make the pipe smaller, the flow velocity will have to increase to maintain the same amount of total volume of air moved. Make the pipe bigger and the flow speed drops, which could mean you are getting less "suction" effect to pull gas out of the cylinder.
Back pressure kind of measures this, but not really in a 1:1 way that makes sense. For instance, you could have a 6" exhaust and crimp the very end of the tailpipe down to 2" and you'd get back pressure, but it would be terrible for the system compared to just having smaller diameter pipe for the whole length.
That aside (sorry, pet peeve of mine when it comes to some old car myths), I don't think a Viper sounds very good straight piped and I don't think you'd be getting the muscle car sound from it. It would be louder for sure, but the Viper engine has a very unique sound and at least to my ears sounds better with exhaust on it. Maybe the cats would be enough to tame it down, but I remember firing my car up on straight open headers after I put them on just because I was curious and it sounded like trash. In my experience at least, the Borla cat back system or the full Mopar 3" race exhaust (basically just a 3" version of the Borla system, but you lose the cats) have the deepest tone and give more of that muscle car sound. The Corsa system seems more high pitched and **** to me and I think the Belanger is maybe somewhere in between the two. I think there are a few others out there as well, but I don't hear about them as much or see them as often. I think Magnaflow has a two chamber system that is maybe on the deeper side of tone, but it's not one I see very often. You can find some clips on YouTube and such if you do some searches for Viper exhaust, though mic quality various all over the place as well as other engine mods, so not always the best 1:1 comparisons.