I was running both P4 and P5 at the same time but I have finally abandoned P4. The bonus about being able to use different runtimes is you can set up a new runtime just for V2 and her clothes and one for V3 etc so you needn't ever have to remember if a particular item is going to fit that character. You just have to be vigilant when installing the characters. Aside from that the rendering capabilities are just so different. P5 will please whether you are are really enthusiastic and want to experiment with shader nodes etc or whether you just want to add a few lights as usual. It's all about what you want from it. Using both, P4 started to feel old but I was used to it. I had the same issue with Windows 3.11 :0)