Much ink has been spilled about the woman caught in adultery, but I think reading it as "this overturns capital punishment in the Torah" is a complete misread. For one, God doesn't change, and Christ is the one who gave the Torah. Why would He reverse Himself and His own commandments?
First, this was a political trap - the Jewish leaders had no authority to execute anyone (see John 18:31) without Roman approval. This is much like the "render unto Caesar" dilemma - if He says don't stone her, they accuse Him of approving of violating the Torah; if He says execute her, they could accuse Him of conflicting with Roman authority as well as perhaps hypocrisy on His own teaching of mercy.
On top of that, this is not Torah correctly applied. In the Torah (Lev 20:10 and Duet 22:22) both the man and woman were subject to punishment. Yet here there is no man. The Torah also requires witnesses (two or three, see Duet 17:6 and 19:15. There is no record of a witness at all, only the accused.
Jesus doesn't say "hey guys, the death penalty is barbaric and unjust" or "the death penalty shouldn't be used for adultery, only more serious matters." He says - if you are without sin, cast the stone. This does not deny the Torah, but the injustice - it upholds Torah. They lacked the witnesses and the authority, and he exposes their own sin. This is a critique of hypocrisy and misapplication of the Torah by the giver of the Torah.
And He tells her to go and sin no more. Part of the death penalty for the Torah is not for sin as such, but for unrepentant sin without repentance - sin with the hand held high. Those people were setting themselves in rebellion against God, and must be cut off. St Paul affirms this, saying - "expel the wicked man from among you." If you go and look at the times when this phrase is in the Torah almost all of them are in the context of a penalty up to and including death. (Deuteronomy 13:5, 17:7, 21:21, 22:21, 24:7). It is not right to say that Jesus abrogates or changes the teaching of the Torah, or St Paul - both deny this explicitly.