Girthmaster seems about 7.5x7. His girth has been measured ~7” multiple times (yes I’m aware there’s always the possibility of cheating, but I don’t think he’d have made it this far with that name if there wasn’t some substance to back it up).
As for length, there was a pixel count posted pages back while his girth is being measured that got 7.5+, although those are rarely perfect. It was a pretty good straight down shot though, so I took the flattest and most neutral/straight down inch on the tape, zoomed in until the inch in the photo matched an inch on my ruler and measured his length at 7.5+. Of course this likely isn’t perfect and I guess you could argue for different NBP start points, but he seems ~7.5”.
As for “sir” or whatever you call him, his girth has been measured multiple times, with the biggest being just under 8” mid shaft. In the clip where they measure his length with a ruler (which was about 8.25 IIRC), she claimed he struggled to stay hard, which I guess makes some sense because his mid shaft girth is “only” a bit over 7.5 there and it seemed to hang down somewhat in that clip, whereas he doesn’t in other instances. I think if fully hard he could be something like 8.5+ x just under 8 mid shaft. Maybe a full 8 at base. Easily the biggest “proven” dick by volume online.
As for Dredd, he doesn’t give much to work with, but ~8.5x6.5 would seem about right.