I don't think this question is well defined enough to be meaningful.
You can certainly get closer than asserting that, e.g., a hand calculator is more powerful than a human brain because it can do 7 digit long division almost instantly.
At some point, we'll have computers powerful enough to run a working simulation of a human brain. Shortly before that, there will be a point when computers of that sort are "as powerful as a human brain", though we might not realize it when that happens if the software lags.
You can certainly get closer than asserting that, e.g., a hand calculator is more powerful than a human brain because it can do 7 digit long division almost instantly.
At some point, we'll have computers powerful enough to run a working simulation of a human brain. Shortly before that, there will be a point when computers of that sort are "as powerful as a human brain", though we might not realize it when that happens if the software lags.
So that's an upper bound on charlesju's question.