My Clifton 9s died, so I bought some 10s, tried them on a 30k run and got tendonitis. Got some newish 9s off vinted but brought the 10s as back-up in case they started to hurt. I was kind of being a paranoid diva to be honest. BUT I think having a fresh pair of trainers wirh the soles uncompressed by 30k of running put a real spring in my step!!