my cab finally got upgraded, however bt checker only showing I could only get unlimited faster unlimited broadband which goes up to 17mb. When I check with sky,plusnet, they all said I could get upto 21mb with their fibre plan. I also checked on openreach wholesale adsl checker, it saids i can get upto 21mb with the fttc.
could someone help me out?
You will get whatever your line is capable of getting regardless of supplier. You are only being offered faster broadband as (presumably) the checker shows you are not capable of Infinity1 speeds due to distance from the cabinet. The line will be capped at 40Mbps but you won't know exactly what speed you will get until it is provided.
Someone correct me here but my understanding is that the most likely speeds will be in Range B.
No, the speeds could be anywhere between max range A and min Range B. Range A speeds are more likely.