Yes 3K is more realistic for a good machine at larger sizes.

What exactly do you want to do with this machine.? Reason I ask is that you mention 1.2m for L,W & D this indicates a long Z axis which for cutting Foam etc is fine. But if you have ideas to use this machine for other materials like wood etc then it will need designing such that the Z extension can be kept to a minimum. . . Best way to do this is with an adjustable height bed .