They are both excellent speakers. It's like anything, those who prefer Focal will say they are better and vice versa. From a sound reproduction point of view, I personally prefer the smoother sound of the Hertz over Focal. It's personal preference at the end of the day, you can't knock either manufacturer.
I will send you a pm, but £400 will not get you what you are looking for, for decent equipment. You can go lower end for that though.