Here's what I did with mine:
-SSD for the system and user directories, connected to the second optical port connector
-Everything else on HDDs in the four bays
-48GB RAM in triple channel config
-X5675 processors to make that memory run at 1333mhz
-Wifi/BT card upgrades (and if you're lucky you can even get handoff support with the CAT tool
-Radeon Pulse RX580 8gb
-Since that card has Metal support, I was able to upgrade to Mojave (but be sure to follow these instructions to upgrade your firmware using an EFI supported card first)
-Pray to God
-Troubleshoot, troubleshoot, troubleshoot
After that you'll get something around 6000 on Geekbench 5. Not bad for a 10 year old machine.