I was really scared to get my septum done but it really wasn't bad at all. It just stung a little and made my eyes water. I'd rate it a 3 or 4 out of 10. It was slightly more painful than my right nostril and slightly less painful than my left... and definitely a different kind of pain than my other piercings. What makes it great is that it's a quick healer! Just make sure you go to a great, experienced piercer who really knows what they're doing so they'll pierce the right spot instead of the cartilage. If they do it incorrectly it will be the most painful piercing you'll ever have!
I have 1/2" lobes and 11 piercings: left helix x2, both conches, both nostrils, septum, navel, and VCH.
My lobes are small but I know a lot about stretching and how to do it safely, so message me if you have any questions!