He is 6+ on the shaft with a big mushroom head. I have never had a problem fitting his head into my mouth and some of the shaft. I quite enjoy it. He says my back teeth have never hurt the head of his penis, which I used to be extremely paranoid about, he says he just feels them but they aren't sharp or painful and I have nothing to worry about with that. He says he likes that sensation.
I have difficulty deep throating his penis because of the width. I can get a smaller width dildo down my throat very easily, but I can't get his penis down my throat when he's fully erect, only partially. I like feeling his penis get harder while it's down my throat, it's such a cool feeling, but once it gets too erect, I can't fit his penis down my throat again. It's very frustrating. I'm working up to being able to swallow him when he's fully erect, but that fat mushroom head is hard to take down. I'm going to be able to do it someday, swallow him when he's rock hard.
He had a size queen fuckbuddy before me who could deep throat him, so I know it's feasible.