It's not gonna get a lot faster, but I suggest switching to Green-Team (like I did a year ago).

Then, it becomes Intel and Nvidia GPU ( with PhysX Co-Processor) for Windows Direct-X12 gaming.

A single nice MSI (or Zotac) GTX-1070-1080-Ti should act as one last upgrade to this old machine.

https://www.dell.com/community/Alienware-Desktops/Aurora-R4/td-p/6089107

Works best with Dell/Alienware 875w Power-Supply.

Aurora-R4 should be running Windows-10 64bit.

EDITED

Thanks Tesla you are awesome as usual.

I will follow your advice and I will take a GTX-1070-1080-Ti video card (switching so to Green-Team).

 I have Windows-10 64bit yet.

Good talking with you, see soon

Antonio