...I think it's unfortunate that the AEBS still doesn't allow attachment of an external antenna...Apple seems to have a thing about antennas.
I am not sold on external antennas. A friend of mine got an ASUS AC router recently with external antenna with the idea of sending the signal to his detached garage which is about 200 ft away. Well, the signal was pretty weak, so I suggested that he got a replacement directional antenna from ASUS which is made for that router. Long story short, the replacement arrived, and with a bit of aiming and playing with power out, it helped boosted the signal about 10% at the expense of signal in other directions in seemed.
However, the ASUS AC router was significantly better than his old N router even for N clients. After his experience and my spending time trying to help him boost the signal, I consider external antenna not that helpful. I did consider making a coffee can antenna for him, but then again I understand if you focus the energy in one direction, you lose if in other directions. The way I see it is that you have X amount of energy to be broadcasted. Unless your router is at one end of the house and the rest of your clients are at the other end and fit in a directional beam of a directional antenna, putting a directional antenna on a router doesn't really help the situation.
By the way, just for comparison I tested my Time Capsule AC against his ASUS ASUS RT-AC66U with external antenna for distance, and the Time Capsule AC does at least as good if not better than the ASUS.
So, I don't know how well the 5th gen TC performs, but if it is anything close to the new one, and if OP currently can get some signal with the old linksys e2000, I suspect the 5th gen TC will do just fine. Just speculating. But this is a long term purchase, so I would go with the new TC because chances are I will be stuck with it for a while and I am doubtful the saving is that great going with the old one.