To what temperature should you take candied citrus peels?
I don't think you are looking for a specific temp (i.e.; crack or soft ball stage) after adding the citrus since you have already "contaminated" the syrup.  My preferred recipe is from Epicurious.com (http://www.epicurious.com/recipes/food/views/Candied-Citrus-Peel-107434).  I have used it twice with great results and am going to be making again very soon for the holidays.