The performance issues. (The Witcher)

All Shalom.That's the problem,the Witcher 1 at low graphene on ultra,the fps is almost the same,30-40,sometimes(in Vizim) sags to 20,while it is steep(frame time jump).I don't know what to do with it.
as I understand it,though the download of the cp and gpu the fact that the game works badly with more than 2 cores and threads.
The load on the core is: 80-20-20-20.Gpu load is 50%.
System:
AMD A8-5600K 4,0 Ghz(+400 boost)
750ti(stock)
8gb RAM(overclocking 1666,the timings do not remember,and they are not particularly important in this problem)
The funny thing is that Witcher 2 is flying at a high(50-60),and the third part at a high 30 fps.
Why is the first part so bad I know,but what can you do,I don't know.