Same here, I'd also be interested to hear if anyone has any tips for being able to tell when the wheel-running becomes excessive! It's so hard to know what goes on in their little hamster brains!
I will say that when I first got my hamster, she was most definitely stress-running then -- and what she would do is make constant laps around the cage including a burst of running on the wheel every time she went past it. So a burst of wheel-running, then off to make a lap of the cage, and back on the wheel again. Does that sound like what your gus is doing?
Is he still coming to the doorway to get treats or not interested at all anymore?
Another thing is, how old is your hamster, because I've heard people say that young hamsters can fare OK in the recommended minimum but then quickly outgrow them. Maybe the cage was fine at first but now feels too small for him?
Sorry if this was not helpful, I'm a beginner myself so just trying to throw ideas out there!