Thats about right,
I had an HP z800 with Dual xeon x5670 and 48gb ram and it geek benched only about 22,000 running Windows-10.
OSX will score lower, But OS X is very stable and reliable . Where Win-10 updates always require reboots.
And Win-10 browser ( edge ) has memory utilization problems.
You can configure boot camp and install MS-Win-10 on your computer and see for yourself.
MacOS Sierra is more reliable and stable.
So a geek bench score of 19,000 to 22,000 is about right for those CPU's
My OEM 2009 Mac Pro with dual quad cores ( 8-cores, 16-threads ) only score about 16,000
I was considering updating the CPU buy did not because it did not appear worth the money.
Did you flash the firmware to 5,1 and put faster ram?
PC-1333 ram ?
32GB Kit 4X 8GB DIMM Apple Mac Pro Mid 2010 A1289 MacPro5,1 Memory Ram 5053772970984 | eBay
More ram and a good graphics card is however.
32gb of ram and an AMD RX580
Sapphire PULSE Radeon RX 580 8GB GDDR5 PCI-E Dual HDMI / DVI-D / Dual DP OC w/ Backplate (UEFI), 100411P8GOCL - Newegg.c…
Check here:
x5670 mac - Geekbench Search - Geekbench Browser