Now I've checked, the CPU temperature is about that of GPU, at around 68-75C. VRAM didn't show me anything unsual there, remaining relatively constant, with reasonable loading and unloading during entering/exiting large area.
After looking at all these, right now the feeling I have is that the system somehow refuses to go too hot and forces the GPU to nearly stop working (down to roughly 20% usage). Drops in FPS make sense because the GPU isn't really working during those few seconds.
So it goes like this. Temperature is high, the GPU stop working, and thus the drop in FPS, and it all repeats again and again.
But the funny thing is, now that I have noticed, the fluctuation starts at around 68-69C, mostly, and the temp quickly drops 2-3C, repeat and repeat... but as time goes, and I'm talking about minutes, the temperature range also begins to rise, going from 66-68 to 72-75, something like that.
So there doesn't seem to be a fixed upper threshold for referencing.
Yet another funny thing, when I was playing Skyrim, the fluctuation is there when I'm in the world, but when I enter a small cell (house, dungeon), fluctuation is gone!! I stared somewhat angrily at the temp, which says 74C

.
I tabbed out for a while, tabbed back in, temp at 58C, and the fluctuation is gone even in the world cell!! Of course, until after it rises back to 68C or something.:angry:
Damn. Fumbled around the NVIDIA setting, didn't do anything in particular. Damn I bought the laptop because the older one has yet another funky thing, and I got myself out of it just to fall into another.