Supposedly the RB-1000 tonearms are meticulously assembled and there are only 2 trained technicians that do this. The bearings are also supposedly of higher quality. I have never disassmbled either of these arms to verify this. The RB-1000 is polished rather than painted and has metal pieces that replace the plastic pieces on the RB-700.
I cannot say anything about performance between the 2 arms since I have never compared them side by side but I do own 2 RB-700 arms and they are quite good for the money.