Upgrading from AC2200 to AX (which is best for my situation)

I have the RBK40 with three satellites. I am looking at the AX6000 or AX4000 series. My biggest piece of dissatisfaciton is that when in the main room with the hub, i am getting speeds of well over 300mbps up and down but in my office (where I spend most of the day), I am only getting 80mbps and it has a satellite in the room. 

With the increased range of the AX tri-band, would I be able to go to a main hub and two satellites? or should I look at keeping 3 satellites? My home is a single story (1300 square feet) and the office is a separate building in the backyard about 30 feet away from the house.