"It's the signal strength that lets it down though."
So when your car runs out of gas, you blame your car?
It is not just about SpeedTest and if it reports low then the LTE must suck.
I installed OpenSignal on my XS. It was quite revealing. I initially also thought my XS just must suck when it came to LTE. When using OpenSignal however, and comparing to the averages that OpenSignal revealed for the given area I was in, my XS was rarely lower than average reported for the area. Mostly, it was much higher even. Now, if a given area was just plain slow, my XS speeds were also in range - it can't create signal out of nowhere. However, again, it was at or above the averages given by OpenSignal. It is hard to complain with that.