My experience was consistent speeds at 1/10 to 1/5 of the promised speeds, slow downloads, and my Internet dropping for at least a few minutes daily.
A few times every week the Internet would drop for a few hours. Worst Internet ever.
I was paying for 15mbps and the highest speed I ever had was 5mbps. 90% of the time my speed was 1-1.5mbps. Their Internet sucks!
After 15-20 years with them I had enough and switched to Comcast. It is FAR superior to Century Link. I haven't had my service drop once and the speed is at or above the promised speed at all times. Comcast customer service still sucks but so did Century Link.