I actually got the number wrong in my first post, I meant 20%, my bad on that - missed it when reading over the post. I don't have the option to check Cuda any more on the performance tab and I don't have a program to monitor it specifically so all I can do is give you these numbers using my normal settings:
Standing just out from one of these spots and spinning around I have utilization 19-20%, 3D usage same, 1.7/6.0gb memory used, GPU temp 50-52C.
Standing in one of those spots and turning my camera the same sort of way for 5 minutes (that's when I notice it happening, when I move my camera) I get utilization go up to 24% briefly here and there for 3D, memory stays the same, temp the same. Nothing seems to suggest that the card is working any harder when I'm in these spots.
For a while I wondered if it was the villagers, but I can walk into the middle of them and it's smooth again. I can look at the same spot from different directions, and it's fine. It's just these patches that are less than a chunk in size for some reason make my game slow down but nothing seems to suggest the PC is actually working any harder.
If you can suggest a program to monitor the CUDA I'd be more than happy to do a test again to see if there's a significant raise in usage.
It's not like this is game breaking or anything, it's just slightly annoying.
Cheers for the reply