What route has better peformance is just the question. I really wanna buy Leipzig Dresden but if the peformance is worse then Nahverkher Dresden I am not gonan do it..
You have said multiple times, your computer isnt the best, its hard to say if the improvements to performance will be noticeable to you. You already judged Frankfurt for the "terrible" performance, so in your case i expect it to be the same for Leipzig, no matter the improvements. After all, using a PC wont limit you in what you can buy, but does in what you can play and this is not a problem or fault of the developers.
I think buying Leipzig Dresden includes the Nahverkher Dresden route, whereas if you get Nahverkher Dresden you will not get Leipzig Dresden I don't think there is any reason to get Nahverkher Dresden separately, unless you want it for earlier versions of TSW
its more like I own Nahverkher dresden already, I want to extend to Leipzig, but I tough the peformance is maybe worse then on Nahverkher dresden. I can run Nahverkher dresden very well, so if the peformance is not making any difference as the old route, then I will just buy it
