The 680's are a big hoe & quite rare as they were a little too big/pricey for the market where an excavator proved a more viable option -also unless it's 4x4 because of their weight they will bog readily/not steer well in dirt/soft ground (ballasting the rear tyres/fitting oversize front tyres on a 2WD will help but not overcome this shortcoming).
Nothing really inherrently wrong with a 680 if you need a big hoe, the motor/transmission/driveline are quite robust/powerful - I recall the one we had was fitted with air brakes which were excellent too -& the hoe/FELcombination has some serious lifting/breakout capacity, the downside is with all that power an unsympathetic operator could often inflicted severe damage/stress on the machine.
IMO a 680 is fine if you've got a special purpose for such a large hoe & it's bargain priced, but purchase in the knowledge a 580 is lot more nimble, suitable & usefull in "offroad" applications around a farm with the 580 a lot easy to source parts both new & reasonably priced s/h - prior to purchase make certain to test thoroughly the "pushing" power of any Case machine too at operating temperature, they're often fine running around on flat ground but put them load & some have no grunt to push dirt, small trees or even run up a loading ramp onto a truck as the torque converter has been "fried" .