III is more raw, aggressive and open, IV is more modern(ish), tighter and compressed. Both are killers and unmistakably Mark af. I personally prefer the III. If I were in your shoes, I’d get one of those depending on your tastes, sell the V, and get a two channel Recto. And don’t listen to all the different color stripe BS because that’s all subjective, the differences between them are minimal, and they’re all killers in their own right.