I only just finished reading page 11 of 36, so I'm going to post this now and finish reading afterwards.
I still have my 256GB iPhone X (unlocked SIM free with qualcomm chipset), and up on Cheyenne Mountain by NORAD we have poor AT&T cell service (most cell services here are poor, go figure with all those antennae on the mountain). I usually have to turn off LTE and use 4G service when I'm out for a walk, and usually need AT&T Wi-Fi calling for best performance at home.
Both have Carrier version 33.2 (modem firmware is different, Xs Max 1.00.07 and X 3.00.00) and iOS 12.0
So far my Xs Max is outperforming my iPhone X. They both have the same signal strengths with either 1 bar of LTE or 3 bars of 4G. I have not dropped any calls with LTE turned on, as opposed to my X that dropped them on LTE often.
4G internet speed down/up
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Xs Max speed mbps 4.64 / 0.66
X speed mbps 1.13 / 0.61
LTE internet speed down/up
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Xs Max speed mbps 0.43 / 3.66
X speed mbps 0.58 / 0.93