I use mismatched tubes all the time. LIke I am currently using a 700 x18-23c tube in a 700x28c tire with no problem. I use tires slightly bigger than the tubes all the time.

I willgo the opposite direction but that means mounting the tire is usually a pain in the ass. If I have a 700x25c tire and try using a tube made for a 700x28c to 700x32c size, it will be a devil to mount but once mounted, it works fine.

I have no problem inflating to tire's rated PSI ratings when using mismatched tubes. Its not so much the tube but the tire that holds the pressure in place.