First, I have every confidence that you and your spouse are going to make the best decision you can, based on the information you have, and that if it turns out not to work out, you will be able to come up with an alternate solution.
Second, I think it's important to remember that, if you conclude that the commute would not be sustainable, given the rest of your circumstances, you will not be shortchanging your DS by not sending him to the gifted school. If the commute creates an unhealthy situation for your family, then you would be harming him by sending him there, at the cost of other, vital contributors to his well-being (and the well-being of your other children--not to mention you and your DH!). IOW, it may be wise to consider whether sending him to a particular school would be depriving him of healthy (physically, emotionally, and mentally) parents and family life, which, in the big picture, is far more important than perfect academic fit.
It's a good living lesson, too, that he is much more than his academic ability, and that everything you've taught him about being a whole, balanced person actually affects the way you make decisions of substance. Whether you end up sending him to the school near or far away, having some access to this discussion about how it affects the whole person could be quite instructive.
