Unfortunately, I cannot express my professional opinion on the matter because I am green at it. But what you write looks logical. A few years ago I spent several dozen hours looking for a solution and only by limiting the visibility I reduced the frequency of the problem .But it did not solve it, and driving for several dozen minutes and a fatal error was irritating for me. Really the Bus and Cable Car Simulator was a game really close to my heart in which I spent thousands of hours and probably half as much on looking for hubcaps on foot To this day, I remember regions of some huge plant that were not optimized and those FPS drops when I was looking for hubcaps on them, where probably even TML did not think that someone would come in there;)
Ah, If only I had a plug for TML .. I would push for a remake of this game with multiplayer with all my might Or, if my professional field was in game development with development background, maybe I would apply for a license to develop this game if it was possible. You can always dream, right?
BTW you are comparing phenom and geforce 30 series cards. However, the problem already existed on the GTX 970. I do not know if it is also a question of the card or the processor, and if the card which series could be the cause of the beginning of the problem