What do you actually mean with performance? The ability to run apps the require a lot of RAM or to be able to run a lot of apps at once? Or is it something else?
I'm not that familiar in the hardware world, unlike software.
Run a benchmark test. I personally use Antutu Benchmark when measuring my smartphone's performance and compare it with other smartphones. The 3D Score is the one I look at the most since I am a gamer. But Antutu tests your phone's overall performance. Give it a try.