The 3 ton stands that we have are quite small for the weight, but at least we know that there won't be any safety issues as long as they are set correctly.
The jack size also affects how easy it will be to lift the vehicle in the first place, a one-ton trolley jack struggles to lift the front of our D2 V8, while the 2.5ton does it much more easily. You still need a fair bit of grunt even then, as the handles are quite short for the effort needed.
Plus, as has already been said, the larger jacks have a higher lift.
If I was buying now, AFTER we bought the Disco, I'd go for an even larger jack and stands, we bought these originally for servicing our two Renault Trafic vans and an Astravan.
Peter