Either single or double digit, it's about keeping your routine going constantly without giving in. Most penis approaching double digits tend to be a bit harder because the amount of blood have to be supplied to the penis at that size can be tough on your pelvic region. Some with a 10 to 12in penis can testify to the amount of blood pumping needed to keep the erection strong and the penis decently pointing slightly out, but mainly down. Most with 10in+ tend to use medication to keep the erection as strong as possible through cardiovascular constriction. So, just a warning. I want to reach up to 9in x 6.3in and stop there. More than that, I have to force my heart and blood vessels to have greater burdens in my later years in life in maintaining a strong erection.