I have to rush some sorry this is fragmented. Your pc is better than mine on both gpu and cpu. I have a an nvidia gtx 1060 and an old 2013 sandy bridge based 2.5Ghz 6core xeon atm.
50Hz Pal/Europe Klonoa 2 patch works the same as the 60Hz NTSC/US version of the patch from Praful.
If you try to force the 50hz patch onto 60hz mode or vice versa it will throughly screw up the game though
You should be able to use better settings than what I use for the 1060 also dx11 is still faster than OpenGL by a little.
and you don't need mipmapping. actually it used to not even be an option the game will run fine with it off.
Also Blending unit high accuracy in openGL will absolutely destroy your fps
This settings run mostly fine on my 1060
I currently do not know of a way to make fire effects work in Klonoa 2. It has something to do with the the IPU/Playstation 2's Image processing unit. The fire and water use something like a gif or mpeg video.
Also this is the build of pcsx2 that I am referring to that does work currently. https://github.com/PCSX2/pcsx2/commit/fa4ae7800b700ce429822abb734a39556035c946