Also look at work by Alan Dixson. There is probably data in his book on Primate Sexuality to answer your question. For certain, humans actually show MORE sexual dimorphism than the monogamous callitrichid primates.
Many thanks! I actually know that some NW monkeys are monogamous, but haven't checked for T baseline nor sexual dimorphism. I don't even know if it makes any sense using T to see aggression
T can enter developmentally or as real-time fluctuations related to social context. Both would be important to investigate. T levels clearly play a role in regulating and/or responding to aggressive contexts in vertebrates, but the relationship between T and behavior is especially complex and not the same in all species. There are papers that quantify relative sexual dimorphism in primates..although I cannot quote a reference now.