Adding drives to 5D3

Right now I have two 10TB WD Red NAS hardrives in my drodo. I was looking at adding a 14 TB WD red NAS drive. My question is that drive has a higher cache (512 mb) then my current ones in the drobo already. Does that matter? Or should I stick with a drive with the same cache size? Does cache size matter?

I was reading that NAS drives are slower the desktop drives? What is the best drive to add to my drobo for maximum space and speed with the two WD red NAS 10 TB drives I already have in the drobo?

The Drobo drive webpage does not recommend mixing HDDs with different rotational speeds for optimal performance, so use your 10TB rotational speed as your guide for future expansion purchases.
There is no issue with cache parity that I am aware of, but take note of the drives that are NOT supported as listed on that same webpage.