This is to my understanding that schools that don't require the Math GRE will most likely not have a cutoff in terms of what you scored. However, since their applications will be based on the General GREs, that will be weighed more heavily. So what does this mean? Perhaps those schools will use cut-offs for the General GREs, and I'm almost certain the Math GREs will not have a cut off. I believe that 700 is roughly 60 percentile, so for MOST schools, I don't think it will hurt your chances. In my honest opinion, if I were in your situation, I would speak with my advisors / academic advisors about this. Also, I would email prospective schools about any cut-offs on the Math GRE or whether to send such score. Though I wouldn't count on them responding or giving a straight answer. Remember, how the admission committee use the Math GRE score will vary from school to school.