We were able to book a category 3 in March for our May 27th sailing. I would imagine weeks like school vacations and holiday book up pretty quickly though.
There are four category 3 staterooms located in the middle of the ship. They have a different layout than the other rooms and they are larger. The stateroom numbers are 8032, 8034, 8532 & 8534. You can see them on the deck plans layout. Unfortunately, we couldn't get one of these rooms, but the standard category 3 was big enough for our family of 5. It was great being able to have 2 people in separate showers while one took a bath. It took us no time to get ready for dinner each night.
Sweetspot: I believe on the Magic, it's called Sessions and on the Wonder, it's the Cadillac Lounge. I called Debbie right after I made my final payment, so that would have been at the 60 day mark.