I have the highest tier unlimited plan, even on the plan without using all my data there's times where it's less than 0.1mbps yes mbps and not MB/s. Then there's other times when it's 8mbps which is fine. However after running out of data I understand they "They may throttle data in times of congestion."
However congestion shouldn't be 24/7 in my local area. The moment I run out of data my speed is reduced anywhere from 256 bytes to 20 kbps until my plan resets after 3 weeks. For those wondering yes that reads bytes as in less than 0.01mbps. I whole heartily disagree congestion lasts for over three weeks at all hours. Checked at 1am, check at 1pm, checked at 5am, checked at 5pm. I've stayed awake and at home for over 24 hours several times doing speed tests to always get the same results showing that this so called congestion is never ending.