I was out shooting some sunset shots the other night, and set the exposure to -2.3 stops. Then forgot to set it back. Oops. Today I came across a gray tree frog, got some nice shots, and didn't realize they were badly underexposed until I saw them on my computer. LR to the rescue, and they turned out reasonably ok (see attached).

Guess I'm a slow learner; I've made this mistake before.

Question is, how much is lost in IQ by this sort of blunder and fix? I'm guessing that since 2^2.3 is about 5, the net effect would be the same as if I'd exposed it correctly and used an ISO five times bigger than I used. I shot the attached at ISO 320 (D7000 with 40mm micro @ f16) and would say the result looks better than if I'd shot it at ISO 1600.