Go based on feel. I doubt you have done a "proper" 1RM. The book tells you how somebody coming in on the first day should choose weights, it's not entirely appropriate in your case, but use that method. It's better to go slightly low and use 10# jumps on the squat for a while than to start high and get stuck. If you start at 165 on the squat, you can probably do 10# jumps until 215#, at least. You could probably do 195 or 200 on your first day, but I'd recommend against it unless you're used to squatting with this kind of volume (3x5, 3x per week). It's a difference of about a week of training, but it makes a difference in how you end up feeling, so don't be too proud.