Alright audiophile jackasses, here's your extended Mofi 45 Folsom Prison review vs the RKS VMP pressing.
The RKS is very well done and beat out all the other modern pressings of this album I've tried. I've not heard an OG so I can't speak to those, but it pretty handily bested everything else I've heard. It's RKS so it's his usual style, it's mixed like a traditional rock record. Everything is punched up a bit, Cash's voice is brought forward in the mix and is now as loud if not louder than the guitars, but his voice sounds great, natural. The stage is fairly flat, not necessarily in a bad way, but it's crankable and every element of the songs will sound about even in volume. It sounds less dirty and live and more cleanly produced, like a messy live session that's been fixed up before release.
The biggest difference to this Mofi 45 is the width of the stage. The Mofi has a much deeper and wider stage, you can place the band members in 3D space on the stage in front of you. You feel like you're more in the room with the band... and the inmates. However it's by no means a huge stage, it's just got more depth than the fairly two dimensional VMP mix. But it's a 45 so it's to be expected that the stage will probably best a 33. In terms of the sound it hasn't been cleaned up as much as the RKS VMP. Levels between instruments are more varied, Cash's voice is recessed in the mix and the guitars and drums are playing over him to a degree. Again not really in a bad way, just a bit more messy and live sounding. I think his voice doesn't sound as natural on the Mofi as it does on the VMP. I think RKS did a great job cleaning up a pretty flawed recording. I prefer how his voice sounds on the VMP to the more rounded and somewhat muffled Mofi version. I'm not even sure muffled is the right word... "Softer" night be a better descriptor.
In the end I think it really comes down to personal preference. I think the 33 sounds great and it's very clean and a fun listen... and you don't have to get up and flip the record after 4 songs. The Mofi 45 sounds a bit more chaotic and live, and you feel like you're more in the room with the performers. However that being said I think that this is very system dependent and that your mileage may vary depending on your rig. I'm not sure these differences would be particularly noticeable on everyone's systems. It's by no means a massive difference. Ultimately I don't think you can go wrong with either.