Its hard to tell. One thing I did notice was they were a bit warmer than the others every time I handled them and more social. As for comb, I had a Jersey Giant and cochin that was so red and big at about 4 weeks, they also had the biggest feet compared to the others but ended up hens. With the three ive had in the last year they were all different with comb, feathering and size, the only thing that was the same was that heat they put off and friendliness.
Now that you mention it, my tiny chick (who is almost definitely a roo) is very warm when he settles on me. I'll have to test that on my Ameraucanas to see if it holds true with them. If it does I may just have to hold all my chicks again to see who's warm.