Well the cpu is calculating every single person and goods package ingame, where the are going and so on. The faster it can access data stored in the ram the better. My guess is that the speed of the ram is more important than the size.
But thb having 4gb ram is a bit 2006. I dont get why new cheap pc’s still come with that low amount. Its just like phones i guess, they want to make as much money selling stuff with 64gb storage before making 128gb once. I bet they could mass produce 512gb sd cards to the point where they was as cheap as 64gb once if the market demanded it.