It's easy to be tempted by the fact that if we went from 600 to 650 with 'x' days of studies, then it might be possible to go from 650 to 700 in ~x days and then onward beyond 700. It's simply not true. Once we cross that 67-680 level, every 10 points is a fight and requires practice, focus, and eliminating all weaknesses in approach. It's sort of a sharp skill curve increase in that bracket.
So if you've begun studying and you aren't the "genius" types (starting off at 750 and feeling pissed because you did not get a 790) then you might want to understand that this is very real for most test takers. There is a sharp upward skill expectation once you come closer to 700. Just gotta study harder.