The issue is right across the defence - As things stand we have Ayling, whose legs have gone: Borges, great attitude but slow for a full/wing back, Fry with the turning circle of an oil tanker, Edmondson (nuff said) and Lenihan who hasn't kicked a ball in the best part of 2 seasons.Is pace really that important for a centre back? Useful certainly. But if you can read the game well and do everything else well, its not essential. Been plenty of top class centre backs over the years not blessed with pace.
If you're relying on your centre backs winning foot races against the opposition I'd argue you've got bigger issues to worry about.
Bangura is quick, but seemingly a perma-crock.
Pace isn't a cure-all for sure, but we are in need of some.