If the tattoo isn't doing it for you, ? , just look at how easily it's fitting into the girl's mouths. A 6 inch girth is a jawstretching sonofabitch, it's about all that a girl can do without giving you serious teeth contact problems and only the talented can throat it.
I've always thought the dude was 8.5 x 6. However, his girth looks pretty "weak" in those pictures. I could've sworn I've seen him thicker. His girth is most likely below 5.75" in those pictures.