It all depends on what cpu model you have?
About ~500 H/s for dual X5690 using xmr-stak-cpu cryptonight miner. Mining Electroneum (ETN) with 500 H/s for a month would ge about 552 ETN / worth $88.
Your electricty bill is probably higher.
Page 2 here shows cpu support list, not sure if its worth upgrading
https://h20195.www2.hpe.com/v2/getpdf.aspx/c04199811.pdf?ver=48