I am glad you managed to get a picture of this onto the forum. It is exactly like what I reported in "Strange horizontal lines .." but I was unable to figure out how to add a snapshot to my post.
My problem is also with a GeForce GT 6xx product line (mine is the GT 640 with 16G). The entire series uses the same driver. There are some differences, however.
1) What level driver do you have (mine is 18.104.22.16843 dated 6/12/2014 19:47:35).
2) When did you last update your driver (I did mine within a couple of days of release -- 6/12 - 6/14).
3) Did you notice the horizontal line affect in the previous build of the game (0.20) -- I did.
4) I found that turning off both "enable bloom" and "enable ambient occlusion". If either of these are on the lines return. Does this match with what you are seeing?
5) I saw this from the start of a new game. I have not progressed far in my first 0.30 game due to trying to narrow down conditions where this affect occurs.
6) I see this affect flicker on momentarily at times after turning both "enable bloom" and "enable ambient occlusion" off.
While this may begin to look like an NVidia driver problem, it could also be a problem in coordination between NVidia code and GC3 code. I think the SD devs should look at this first, then bring the NVidia devs into it if their help is needed.