I've never actually been on IV antibiotics. I don't know my FEV1. My recollection is that I used to have a loss of about 1% to 2% lung function when I used to have a hole in my left lung. I haven't seen a doctor recently, but I know by how my fingernails look and the improvement in my feet (etc) that my lung function is better than it's ever been in my life.
I don't mean to be rude. I thought about not replying at all because I know I am way outside the norm for a CFer. But I do have (atypical) CF and that's one data point for you, fwiw.