thanks for your input guys, that's much appreciated!
So if I correctly interpret your thoughts that green brick is more a thing of hype rather than performance and my best bet to improve and experiment would be to stick with Rika, Chosera and Gesshin stones. (Bester maybe?)
I'm not so sure about JNats, they kind of "intimidate" me, meaning they cost quite a bit and I'm not sure I've got skills to fully appreciate them.
How would you suggest I enrich my current setup, i.e. - if you had to buy one or max two stones on top of what I've got what would you go for and why?
If that helps my knives are a Hattori HD gyuto (vg10@61 hrc), a Yoshikane petty (SKD11@64 hrc) and a Felix german chefs (x50CrMoV15@?)