Since I treat most trips as solo, even when I'm with others, I can't really describe a system. However, I'm really glad to see this thread - sharing gear is a topic that doesn't get discussed much here, and it is a great way to keep pack weight down. However, it may not reduce it as much as it would first appear. For example, only carrying one tent is lighter, but it will be a two person tent. That tent will weigh less than two one-person tents, but not half as much. Likewise, you won't be carrying two stoves, but you will carry a larger pot (or more pots) and probably will need bowls and cups since you won't eat and drink from a small pot. (You won't need the bowls if you eat from the pouch, though.) You definitely won't need two filters, so that's pure savings.

I do have a couple of comments about your technique.

If you become separated overnight, the packing methods you describe could mean that your wife would have no shelter and nothing to eat; you would have shelter, but couldn't cook your food. In your case, this may not be a problem if you and your wife have a strict rule about always staying together. This seems to be a common rule among most of the husband-wife (boyfriend-girlfriend) or parent-child teams I meet, but not among the friend-friend teams. (In fact, this is exactly why my friends and I treat our trips as solo trips taken together.) So, if you're not committed to staying together, it might make sense to ensure you both had some of the food, and that the person without the tent had a groundcloth or small tarp.

My other comment relates to how the weight is shared. I'm assuming that, in your case, you and your wife are equally fit, and so the 60%-40% split seems appropriate since you are physically able to carry more weight. However, I can think of cases where the opposite is true. One of my female hiking friends is physically smaller than me, but extremely fit - strong, athletic, and very active. I, on the other hand, am about 10 pounds overweight and only average fitness. If we were sharing gear, and she were so kind as to offer, it would make a great deal of sense that she might carry 30 pounds while I carried 20. Such a situation might also exist where one partner had a physical impairment (such as asthma, or bum knees/hips, arthritis, or shoulder injuries.)

There is no right way or wrong way to divvy up loads - it depends on a variety of factors unique to the people sharing the gear. Thanks again for telling us how you and your wife do it; I hope you've started a very productive thread on a somewhat neglected topic!