The 701 is supposed to be one of the best TTs manufactured by Dual. It is considered a classic. It is heavier than the 704 and more stable. There are rumours that by the time the 704 had come out, Dual started cutting costs and the quality of the motor went down.
Pick up both, and keep the 701. I am sure you can easily sell the 704 to a avid TT-phile on HFV.
I am not sure about the 700 series, but the Dual 606 I had worked superbly with an Ortofon cartridge (it was the Concorde model, if I remember right)
Cheers