First i need to say, that i have a new machine, where all these problems began. With my old machine all i have had was just low fps in late game. Now game run perfectly, just with an exception, that late game low fps is replaced by rendering issues, which lead to freezing and forced game quiting. But what is worst is that, sometimes it corrupts savegame file, so that is many wasted hours and anger for good game abortion almost before the end( or in interresting and funy situations). I will be glad for every advice, but i don't want play it on minimum setting, so i hope, that there is some way to prevent this.