If you are working in the Big 4 that I think you are, then whether you sign or not doesnt mean too much. HR, your counselor and your roundtable committee will see the review no matter what. What will really help you is that you should comment on the review on the things you dont agree, make sure you list them clearly and with the proof to support your argument. Then bring it to your counselor and HR directly. Usually HR is afraid of "people issue" as they may cause lawsuit, so if you mention conflict between you and your senior/manager may help.