The studies regarding Argon are contradictory.
I will tell you my personal experience, and how I came to my conclusions. I have dived Argon, and I have dived airgon (what happens when you top the argon tank with air) and air in a secondary suit inflation bottle. I have done them on consecutive dives, in the same water conditions. I concluded that argon made a noticeable difference in comfort. I subsequently did a lot of diving, some of it with backgas inflation (not helium) and some of it with argon. It seemed pretty consistent that I was warmer with Argon.
The studies really aren't overwhelming. There's some evidence that the best use of Argon is to purge the suit with it before diving, something most of us are neither equipped nor willing to do.
I will tell you that, if Argon helps a little, a heated vest helps a LOT.