In this case, you'll stay with P5 forever, as the C4D features (render, lighting, shaders, etc) improve and update with much faster pace than Poser's.
The distance between them will only get bigger as time goes by (unless, if Poser is aquired by a fast-improving company like Maxon.)

Since you also see C4D as a standard for Poser to catch on, a better investment, if you have the money, is to go for Cinema4D + Interposer pro plugin, which lets you morph, pose, light, texture, model, animate and render Poser characters all inside C4D with far better render speed and results.