I don't bottom so that is one I can't answer.
I use shots now with regards to erection strength, so my decision would place the size at the limit my other half could take and be comfortable. Because I can't have what I want I have no idea what that is, and it would be something I would rather explore if it were possible together with him. A penis growing over time has it's erotic aspects in and of itself. I am already thick enough, but I think a couple more inches in length would be something I would welcome.