Cup springs are firmer and slightly lower, not noticeable though, we're talking mm.
It's either 3 or 5mm I can't remember exactly, it's not 7mm though. Not that you'd notice anyway.
172 springs are the same as far as I know.
when i bought my ph1 it had cup springs on it, so yea they do fit, it looked exactly the same next to my mates standard ph1 though
I'd get eibach sportlines personally. They're a big improvement over standard. Cup springs will make hardly any noticable difference. Not much lower or stiffer.
Thought it would have been slightly lower