My son, Corban was born at 39 weeks and was just 6lbs 4oz so I can't really speak to whether big babies are harder to birth. But I would suspect it's harder to get a bigger baby out. My midwife predicted my son would be on the smaller side, she said that because Asian babies are usually smaller (I took it with a grain of salt since I am caucasion and my husband is Indian so technically our son is only half "Asian")

That said, my advice for anyone preparing for birthing is to do you pelvic floor exercises and continue doing exercise throughout your pregnancy because the better shape you are in the easier it usually is.