Your processor is too weak for this graphic card.
What would be the best/ top NVIDIA Graphic Card for a Studio XPS 8100, Intel Core i7 -870?
If they physically fit (and you have available PCIe-Power-Cables) my guess is ether the Nvidia-970 or even the GTX-1060 will work.
I believe the XPS-8100 is non-UEFI (ie Legacy) BIOS/motherboard ... just like my old Alienware Aurora-R1 with Intel i7-930. Mine is still running great with a GTX-1070. I can run Fallout-4, Fallout-76, and Forza-4 on it with no problems at 1080p.
The GTX-1070 ended-up being much better, faster, and gaming-capable than it's original AMD-5870.
Finally, to offset the CPU-speed (and other older components) your bootable C-Drive should be a SATA-SSD.