Yes, at this scale, dividing by 5.5 is the right thing to do. One thing to pay attention to is your boil equipment differences. A different pot can lead to a different boil-off rate. It wouldn't hurt to run an experiment and see what your boil-off rate is for the pot you intend to use. Even if you get it wrong, you could still boil longer or topoff. But with AG and the opportunity to do a full boil, it's less hassle if you can predict it right. Also, you're going to need a decent scale to measure hops accurately at those quantities.