What size finish or offset disc?

How big of a finish disc or offset disc do you think my John Deere 6120r 4x4 without loader will pull? The ground is flat to slightly rolling, with a clay silty loam mix. I am thinking about buying a large hydraulic fold tandom disc 18'-24' wide. My gut says it won't pull it, but I plan to buy a large cheap tillage tractor one day so if it doesn't pull it I will just keep it folded up. Is that a bad idea?

What size finish or offset disc?