i've seen some of his recent clips and I'd say he's right up there in the top rank for size. Interestingly, if you look at Fashionistas (from John Stagliano) he isn't as thick as he is now. And in joey Silvera's Anal Service 12 he's clearly outcocked by the other guy in his 3some barn scene. (Anal Service 12 also features Aimee Donovan in a group scene with Mandingo). Helpfully, joey gives no details on the male performers. The other guy with Billy Glide is in the last scene with Guage and Cynara Fox. He has an immense cock - he's also in Feeding Frenzy 2.
Anyway, Billy's clearly been popping the right pills and doing the right excercises coz he's very large now - particularly his dickhead. Still, a complete twat though like so many American performers. Ramon is another example of a guy who's got considerably larger.