An offset disc, by it's very nature and design is MUCH heavier than a conventional disc. They are extremely popular for working recently cleared ground. BUT.... That very same wieght that makes it work so well, will stop a tractor dead in it's tracks, should in not have enough power or ballast. A local excavating contractor has an offset disc he pulls with a D6 crawler. It is about 8 or 9'. It seems to be a load on the Cat. crawler. Also, there's a type of disc known as a "bog disc" that would work well in roots, rocks, and ruts... A disc would roll over obstructions, where-as a chisel plow would hang up on things like that.
I'd opt for a heavy disc if one's available. John