That data from the x-plane widget on the screen does not measure only the CPU load, but the combined CPU/GPU load. Instead for CPU load use coretemp and for GPU something like MSI Afterburner. You'll notice the GPU Vram is very often full, even if you are equipped with 4GB... Many of the FPS problems come from that: if the GPU VRAM is full the system bus is overloaded by data in/out managed by the CPU, that also in this case will be not really much loaded, even in complex sceneries. And so the GPU will be waiting for data from its VRAM, constantly full.
The fact is: if you do not have enough VRAM the problem stays there and you'll have to reduce the textures quality to mantain CPU and GPU at a good level of workload, otherwise all the power of this components will never be unleashed.
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