Would appreciate a link to your researched aerial and router. I'm sitting in the country with my phone in a metal kitchen bowl (DIY aerial) for maximum signal, and think I could benefit from some technology!
Take a look at the Teltonika RUTX11[1] with a MIMO LTE antenna from Poynting[2]. Not cheap, but certainly got good results with it. I used Cellmapper[3] to check where the closest tower was.
I have heard that the Huawei ones that accept external antennas are also decent, be it with a much smaller featureset.