Do you believe there's a correlation between romantic callousness and how fast you move on to another partner?

Not necessarily.
People move on in different ways. It doesn't make them a bad person.
It could also be how they were raised. Personally, I can really hold a grudge. I dated a guy for 7 months and was in love with him, then was over it in a month. Its taken me as little as a day to get over someone. It doesn't mean that I am mean, but my whole family, when we are pissed at someone or each other, we just won't talk.
So that's what I do, I just shut it off and that's it.

If it was a long term relationship, as in two years or more, I would probably be hurt if my ex moved on in two weeks. Some people do the rebound thing and jump in quick because they're lonely and hurting, some cause they don't care, some who had met the new person before the previous relationship ended, etc. Other then that, I don't think it means anything, who moves on first. Too many variables. Right place right time you know?

Probably, because a person who didn't invest very much is going to find it easier to move on. That being said, a person who doesn't invest very much might enjoy being single, too.

It's funny that the guy below said girls move on faster, because I personally think guys move on faster because they don't really get involved with girls personally ... only as a combination of parts that are easily replaceable with a different model. Whereas girls tend to fall for guys for who they are as a person and it's hard to replace them with just any different guy.

That being said, clearly it's all perspective.

I feel like women move onto other relationships quicker than men. Women do not like to be alone and will find another guy to get over you. Guys go out and find women to have sex with to get over their past relationship. Just my experience.