Honestly I don't think there's any reason to think they would be much different behaviorally, we know at least 3 species of human have mated in the past. They also existed well into the time period of modern humans so I would bet we mated with them too but it may not be easy to tell in the genomic record. They probably wouldn't mate unless they were similar in many ways, but mainly behaviorally. Classifications that distinguish between different species of human are mainly physical differences, this leads me to believe that ancient human species were much more alike than we would be led to believe by our current colloquial definitions of species.