I have several trees I have been planning on for over a year. They were 10-12 feet/3-4 meters high, so I cut them off last year, waited a year, and have been digging them up and putting them in huge pots - huge meaning something that will hold as much root ball as I can dig up. Most of the pots are 18"/ 1/2 meter across and at least as deep, some larger.
Last Saturday somebody showed up at the bonsai work group with a trident maple that had been 15 feet/5 meters tall two days earlier now was 18" tall, and sitting in a bonsai pot maybe 12"/ 1/3 meter long and maybe 4"/10 centimeters deep. She said the person whose yard it was in had done this many times before and the tree will do fine.
That seems like a lot of root chopping to me. We'll know a year from now.