If you plan to upgrade your pc new cpu on which you want get some xmr then AMD Ryzen is great choice - they have a lot of L3 cache. So even Ryzen 3 1200 will perform about 250H/s. To get more details you can use http://monerobenchmarks.info/singleCPUAMDINTEL.php. The main rule - 1.5-2M of cache per thread.