Haven't had one of these for awhile. This thread is for questions or comments that you've felt silly about not knowing/understanding. Let's try to exchange info that seems obvious, knowing that due to the illusion of transparency it really isn't so obvious!
Lorentz ether theory is a good predictive theory, but I don't want to say that ether is real. In general, if there's a better theory currently available that doesn't include property X, I'd say we're justified in rejecting the reality of X.
I do agree that if there's no better theory currently available, it's a bit weird to say "I reject the reality of X because I'm sure we're going to come up with a better theory at some point." Working with what you have now is good epistemic practice in general. But it is possible that your best current theory is so bad at making predictions that you have no reason to place any substantive degree of confidence in its ontology. In that case, I think it's probably a good idea to withhold ontological commitment until a better theory comes along.
Again, I don't know enough about IQ research to judge which, if any, of these scenarios holds in that field.