I think the z3 line is much better than the Z customs of old. But only in the crashes (which actually was a huge improvement) in fact today i just bought a Z custom power ride over the new z3 rock ride. the z3 rock ride will probably appeal to more people its ping is more silvery than what i bought. My z custom power ride has a deep penetrating ping with a touch of silver. Like i said, the biggest improvement was the crashes, they went above and beyond to make these sound better t han the z custom rock crashes which i thought were harsh and horrible. the medium crashes are the only crashes i have tried and they are very nice. full, bright and cutting. the hihats im on the fence about cant tell you if i like them better now or the z custom mastersounds (which i owned a couple pairs and loved them) but i play a master sounds.
overall the z3 line is a bit of an improvement "overall" but with regards to crashes, a HUGE success. dont know about the china's, never got to play one.
The hats and the crashes are perfect for metal and hard rock. The ride and chinas are a bit too much. The zildjian line has many options in those areas though. If I was a metal drummer I would use rides as crashes in the A custom line,