Is the RAM a mix of third party and the RAM it came with from Apple? What slots were the RAM installed in? Is it running at full speed?
There seems to be an issue when mixing the RAM that came with from Apple and third party RAM which can cause performance issues and may explain the lower scores. The 10700K should be scoring in the mid to high 8000's for multi core and high 1200's to low 1300's for single core.
Interesting - it is 64GB (2x32GB) I added in myself to the base 8GB (2x4GB). All running at standard speed. Slot 1,3 - 32GB, slot 2,4 - 4GB
There seems to be a wide variety of GeekBench 5 scores for this iMac chip - https://browser.geekbench.com/v5/cpu/search?utf8=✓&q=iMac20,2 - first page has results from 6600's to 8800's so I suspect a bit of thermal state, other work running etc.
If I get a chance I'll pull the standard RAM and try again - not worried about losing 8 from 72!