I guess it varies from bike to bike. Because on my frame, the big ring to small cog has a more angled chainline than big ring to big cog. I have a 48/36 pair in the front and an 11-32 cassette, and will routinely use the 48/28 for extended periods of time (as there is no combo with the 36T that falls on that ratio.) The only no-go combos are 36/12 and 36/11. The chain gets chattery (mostly from the absurd amount of slack,) and there's really no need-- 36/12 and 48/16 are the same thing.

Oh, and if the derailleurs are adjusted properly, you should be able to shift into every cog on either front ring. Mine will, and I set it up knowing next to nothing about it, and operating by trial-and-error. As a wise man on here once said, "It's a bicycle. It's not that complicated."

So... you do like 16-22mph up these hypothetical 10% grades? Because that's only guessing at 50rpm. If you're powerful enough to turn the gear at all, you should be flying up those grades like a rocket. Myself, I humbly manage about 7.5mph up a 10%, turning say 50-60rpm in a 48/25 or 48/28. But I am a mere mortal.