I have a G0602 and I definitely favor keeping the full pulley set. Many who do the VFD conversion elominate the intermediate pulley, relying on the VFD to provide the lower speeds. My position on this is that reducing the speed with pulleys also increases torque proportionally. Most VFD setups suffer from lack of low end torque.
It is a simple fact that torque is the product of horsepower and speed. Horsepower is fixed by the amount of power the motor can accept so reducing speed means a reduction in torque. The stock 602 has a 1 hp motor and a low range spindle speed of 150 rpm, it has a pulley ratio of 11.5 and 35 lb-ft., less losses. A 1 hp 1725 motor with VFD operating without the benefit of the intermediate pulley and on the low range would have a pulley ratio of 2.4 and if the VFD dropped the spindle speed down to 150 rpm, the available torque would be 1.5 lb-ft., again less the losses.
I am in the final stages of converting my 602 to a 2.5 hp dc motor with a variable speed drive. I have an encoder on my drive with a feedback loop that senses a decrease in speed with increased load allowing full power to be applied if necessary to maintain speed. which will provide me with an estimated 36 lb-ft of torque in the low pulley setting with spindle speeds as low as 15 rpm.
In the high pulley setting, my spindle speed will have more tha doubled that of the stock setup at 5600 rpm. This is due to a motor running over 4000 rpm.