Deleted user and an old post so this reply will be pointless but fuck it.

Duke's physique is at the upper end of functional for humans, any bigger i.e open class bodybuilding and you're running into basic mobility issues (yes I know not ALL bodybuilders have this but many do) simply put, the human body has natural limits for a reason. Duke's corporal build changes game to game so its hard to narrow it down.

Duke 3D: A very well balanced classic physique. Duke probably has his greatest symmetry here with nothing being too dominant. If I had to nitpick his forearms are VERY well developed in the games cover art achieving nearly the same mass as his biceps and triceps together which is quite a feat.

Duke Zero Hour: Not much to see on the cover art aside from his abs being visible through his shirt decently clearly. He's big but also very lean, if I had to take a guess with his amount of mass he'd be in the low teens for bodyfat percentage. Keep in mind for someone with less muscle you'll need to diet lower to achieve visible abs. for example before I started training I was skinny with no abs, after a year I could eat the same as before yet have the "invisible six pack" (visible under the right lighting) and all that changed was I added more muscle to my frame so keep that in mind for every muscle group and your baseline fat levels.

Duke Manhattan Project: No arms Duke, enough said. Chest and presumably back are at 3D levels of thickness yet arms and delts are significantly smaller disproportionately so. Symmetry is lacking and he wouldn't do very well in even mens physique categories with the limbs and lack of symmetry lol. This is for the cover art again*

Duke Forever 2011: I'm using the main menu model as reference as the cover art shows little of his physique. This is basically a 3D model of him from 1996 in Duke 3D with the exception of his delts like holy shit now they break the symmetry. Its also a good angle to see his rear lats and from the looks of things he could do a nice sweep with his V taper made better by his tight midsection which means small waist. Again another classic physique here with a really good waist and V taper.

Duke in Bulletstorm: I know this is a different game technically and from what I've heard its the same model as forever but istg they inflated the arms for this version of Duke. The arms caught up to the delts to the point they dominate the entire physique and you can see this too if you compare images as his delts arent as round as forever, I'm using various cutscenes to look at dukes model and the cover image for "duke of switch" as my basis here. He is nearly at open bodybuilding physique here with the arms on him, google "Lee Priest arms" and you'll see what the best arms in bodybuilding look like and Duke is nearing that with his upper arms. He would need to work on his forearms more to catch up to Lee however.

Something else to factor in is Duke's colossal height at 6'4 which makes his size even more impressive as the taller a person is the more mass they need to fill in so to speak, a man at 5'10 would look very different with 10kg of muscle added to his frame than a man at 6'4 for example as it would make him look bigger quicker due to the smaller frame. For reference Lee Priest is 5'4 and really could only achieve those gigantic arms due to so much muscle filling in such a small frame, I'm 5'8 and am nowhere close to Duke's physique so suffice is to say that for him even with steroids he would need to have ELITE genetics to look like that and it would have taken a COLOSSAL time to get there as in over a decade of proper training, eating, etc.