The commitment to equality should not be based on any assumption about 'mental capabilities'. Supposing (against the general scientific consensus) for the sake of argument, that you could show that women had on average less 'mental capabilities' why should that lessen our commitment to fair evaluations in employment or an equal consideration of interests?

We think people should be treated equally not because they are the same, but because they deserve equal consideration. Women are people and they deserve to be treated as such. Frankly the way I see it the cost of dehumanising half the population is far higher than potentially employing people who belong to a group that has on average less 'mental capabilities' than another.

Further unless your study shows that all men have stronger 'mental capabilities' than all women* it still makes sense to evaluate on a case by case bases and not generalisations, even if we only think about hiring the 'best' person for the job. To pass over someone who is talented because they happen to be the same gender as people who had a lower average score in some intelligence test doesn't make sense even thinking only about getting the best person for the job.

Science can tell you the way things are, but not how they should be. There might be biological sex differences related to intellectual capacities, sure. But what we are certain of is that humans in general operate with irrational biases and prejudices, such that even in the absence of such differences, people will be treated unfairly.