After installing Exterior Actors Have Torches, now when I load my testing save in Hawkhaven I get a clear-cut transition between pre- and post-torch. My save is at night, and once they receive and light their torches, I see an almost instant 6-7 FPS drop. Depending on my distance from them and how many light the torches, this can vary a fair bit.
Monitoring my system stats, neither the CPU nor the GPU come even close to running at 100% (with CPU, that's by actually watching each core individually). I have a quad core 2.8 GHz intel processor and a Radeon 4870 with 1GB of video memory. It's hard to imagine that torches are intensive enough to make me lose sometimes up to half my pre-torch FPS.
So my question is: why?