I installed windows 7 ultimate on my ryzen system because gaming performance is much better than on windows 10 but the problem is that it keep crashing after 1 - 2 hours, even after everything is installed, ryzen chipset and windows 7 updates. It seems to work stable on windows 10 but the gaming performance is very bad and I hate that.
Ryzen isn't officially supported on Windows 7. Your question would be better asked in the forums of your motherboard manufacturer.
your BSOD must be D1 IRQL_NOT_LESS_EQUAL pci.sys isn't it ?
if that is then your BSOD was exactly the same as my threadripper 1920X which I also installed Win7 Pro if you wanna test you can use HD Tune Pro to do the error test and benchmark your hard drive if BSOD happened during the testing it would be the chipset driver and motherboard problem