So I built the rig with Ryzen 5 1600 (without X) - and was quite amazed. That thing is performing even better than my other 1600X CPUs I get stable 560 H/s from it - again at 3.8 Ghz. I guess it was a lucky pick of the CPU.

If You get below 500 (around 450 H/s) on Your 1600 CPUs - I may know where problem is. Im not sure if I should tell You - cause Youll be taking away my profits by mining better But I am a good person so Ill tell You. (You can alway send me some monero scraps to: 4JUdGzvrMFDWrUUwY3toJATSeNwjn54LkCnKBPRzDuhzi5vSepHfUckJNxRL2gjkNrSqtCoRUrEDAgR wsQvVCjZbRwc3EtMhPPX3gZ4daM )

1st - follow this guide and unlock large pages in Win (https://www.usxmrpool.com/#easy_mining_guide)
2nd - cause You have 8 possible threads (16 MB L3) - but just 6 cores - it DOES matter on which cores You do the mining. Cause two cores will be under heavier load. And Windows uses cores from "beginning" - so usually core 1 and 2. If You put 2 threads on these two first cores - Youll see lower hashrates.

so configure xmr-stak-cpu like this:
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 0 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 2 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 4 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 6 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 8 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 9 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 10 },
{ "low_power_mode" : false, "no_prefetch" : false, "affine_to_cpu" : 11 },

when I had it 0/1/2/3/4/6/8/10 - my hashrates were in those 450 ranges

hope it helps