Cycles: GTX and RTX on the same computer

Over the years I’ve upgraded to my 10 years old workstation to its limit. It’s running fine before RTX 3080 ticame out…It makes my workstation (GTX 1080ti + GTX1070) feels like a turtle when rendering Cycles animation.

I remember reading about RTX 3000s also needs a high end modern CPU to take a full advantage of its rendering power. I wonder if I could just add a RTX 3070 Super or higher model to my old Xeon workstation for Cycles rendering?

My workstation specs:
x58 Mobo with 3 PCI Express 2.0 x 16, one slot left
48GB RAM
Xeon W3680 OC 4.3Ghz
GTX 1080 Ti (liquid cool) + GTX 1070