I have a 920 which is very similar under the hood save for some minor differences. (like the camera)
Performance is good, my 920 runs quite well, does what I need it to do with minimal fuss.
It's not going to destroy today's Lumia 930, the Samsung Galaxy S5 or whatever in benchmarks, but it runs well enough.
Games run smoothly for the most part.
The front facer of my 920 leaves quite a bit to be desired when out-and-about. I don't know if it holds true for the 1020.