I'm totally guessing here, but it sounds like it may be something wrong with your ram.
Can you give me as much details as possible about your ram, its brand name, is it overclocked, etc, I know you have a i5 2500k (i have the same btw) and have a Gigabyte Z68A-D3. ( i got a asus p8 z68)
After a quick google search, here a interesting page. http://www.pcextreme.net/news/your-ram-check-it/
I will quote this part:"One last tip
Another thing to try would be to test one stick of RAM at a time. and test the stick(s) in each DIMM slot to rule out the possibility of a faulty slot, while also providing you with an opportunity to verify you’re using the correct slots for dual-channel operation."
Now if it was my pc, I would do that exactly, I would open it up, take out one stick and put only 1 stick in the A1 slot and test the game, see if it crashes, then test the other stick in same slot then do the same test with the b1 slot, if it crashes only on one of the sticks then there is your problem right there, one of the ram sticks could very well be at fault or if it crashes only in one ram slot then your motherboard's ram slot is slightly faulty.
This is just my opinion, I'm not telling you what to do with your pc especially if you are not very good with hardware.
Dof for me has never crashed unless it was something inside the actaul game developing it that caused a fatal error, which is none of what you mention. So this has to be either driver related, software related(doubtful), or hardware related. And from what you told me about unit selection and wall upgrades, those things instantly dump around 120 kbs or more into the ram to create data tables which lead me to think it is your ram at fault. But again I'm not a super computer tech, correct me if I'm wrong.