IMHO nozzles and engines are secondary respect to radar presence on the 2° protoype, of course would be fantastic if China were already testing such advanced engines, but my impression is that China has more a problem of "quantiy of the quality" than pure quality so they would be better working hard to make j20 operative as soon es possible. For example if china will produce from now to 2020-2025 tons of j10b complemented by a rising number fo j20 China would finally became an airforce superpower. On the other hand if j10b is produced in limited quantities and j20 will be mass-produced far after 2015 they will be weaker.
For now, it is great if this is the second prototype, and very nice if it has a radar on it.