Read some posts and understand they are exactly same hardware, the 670 has more memories and processing power. but when compare the receive sensitivities at each modulateion level, seems ptp 670 is 4 db Less than ptp 650
The sensitivity of the 4.9 GHz to 6.05 GHz variant is the same as PTP 650.
The PTP 670 User Guide covers both variants, and the figures quoted in the original post are for the lower frequency variant. In most applications, the higher frequency variant is the one to use.