I think Sobel's fourth objection is confused about what an idealized/extrapolated agent actually would want. If it had the potential to such perfect experience that makes the human condition look worse than dead in comparison, then the obvious advice is not suicide, but rather to uplift the ordinary human to its own level. This should always be possible since we must already have achieved achieved this to create the extrapolated agent to make the decision, so we can just repeat this process at full resolution on the original human.