danielm175 :
What's the best software to benchmark my system ?
It's the software you use that you should benchmark with.
If you are just looking for a justification for your cpu I'll write you this:
The 7900x win in every single way when there is need for all of it's cores to be used or at least 8. However none of your programs do so, so whilst a benchmark like cinebench will show you it's better in the multicore test it will be worse in the single core test which is what you need more. None of the programs you use can use more than 6 cores so the 7900x with it 10 cores and 20 threads was indeed the wrong cpu to go with.
If you want your money back for it because you need it then go ahead and return it if not just keep it. Don't expect it to get better with time however. By the time games are using thos 10 cores your cpu will be far outdated. A good example would be the I7 980. It's a 6 core from 2010 and unless you do a good oc on it it will struggle to keep 60 fps in new games even tho all of it's cores are actually being used.
Amd did a similar gamble with the fx 8350 but that one is even worse of than the i7 980 due to the terrible single core performance.
tl;dr You bought the wrong cpu. If you want your money back and get something cheaper that would be better for you, you can do that. If not just keep it.