I read different numbers for how much you can milk out of a specific aperture. I am considering a 7" APO.

Some people say 30x per inch, thats it for detail. Well, thats only 210x which seems conservative for a 7" APO.

Many people say 50x per inch, and thats 350x for a 7" APO, sounding better.

But on nights of superb seeing, how far can you take a superb 7" APO, like a TMB or an AP? Can you view Saturn at 500x? 600x? When does decreasing brightness become a problem, and when does additional detail fail to appear?

Thanks
JB