Hardware: 1020 better than 1520 with large aperture, bigger sensor, Xenon > led, same IOS, same Zeiss. CPU only make 1520 take the photos faster, not better in IQ
Software: now, 1520 better than 1020 with Black and newer algorithm. But in the future, 1020 ll go with Black and the same algorithm, maybe with RAW support like 1520.
So, with better camera hardwares (not CPU), I m sure that the photos on 1020 will be better than the photos on 1520.
And I can see Nokia divides 1020 and 1520 for 2 different end-users:
1020 for photography
1520 for business man