Linpack Extreme or Ycruncher. Linpack places a heavy load on RAM and CPU. Ycruncher puts a load on RAM, can't remember how hard it hammers CPU but probably a decent amount.
For pure CPU, OCCT or Prime95.
Cinebench, 3DMark, PCMark and MemTest. Ultimately though just use the pc for whatever you use it for that stresses it. I generally don’t find stress testing that useful beyond a quick indication if it might be stable.
I'd say a combination of Cinebench 23 and 3DMark, then a few "intensive" apps that might be used (e.g., Handbrake). I don't find stress tests like Prime95 useful in this scenario unless it helps you sleep better at night.