Vauxwall does the job but is the least good of all the walls mentioned. Air conditioning is it's main benefit. Even if just bouldering I would rather go to White Spider or Westway. Bouldering is pretty good at White Spider, nice roof, nice big training/circuit board, last time I was there they were in the process of building a new comp wall bit so it's probably even better now. I've never cycled along the A308 but you'll probably be fine.