I used until May a Sony Vaio Laptop Core i7 2GHZ and 8GB of RAM (2012 machine), the computer was working aroung 60 to 70% of CPU usage with the cooler active all the time.
I move since June to a brand new Lenovo Yoga 720 Intel Core i7 7700HQ 2.8GHz and 16GB of RAM the computer works all the time around 20 to 25% of CPU.
I am now using RB 5 that consume less CPU then the version 4.0, I have the DVS and Video functions deactivated at this moment but soon or later I am going to try video for sure.
The memory consumption is around 33%.
Based in these experiences (2 computers and 2 versions), I can say that you need a good computer, less than before version 5.
If you already have a Core i7 with 8 GB of memory like me, you will be able to use DDJ-RZX then you can upgrade your computer to a more powerful one.
Concerning DDJ-RZX I answered a question from other colleague in a previous post
I hope it helps you to decide.
Good Luck
Sergio