Cpu slower after 10 min

I have the exact same problem, also using a 9900k.
After some uptime the defender realtime protection keeps sucking cpu performance.
Have you found any solution for this?

 

That is not what the findings of this thread came to.

 

Yes disabling real time time protection boosted my cpuz-score (and other benches) by about 5%.
With realtime protection I got 5750ish, without 6125.

Funny thing now after disabling CSM and booting on uefi the score went down again only by a small margin, from 6125 to 6040.

Edit: I considered I don't need that real time protection on this machine.
Not using any pirated crap, no weird downloads etc.
And defender still does it's file scan every day so should be ok (hopefully).