You make certain kind of assumptions, you reach corresponding conclusions; you alter the assumptions, then you reach different kind of conclusions.
Well, if the numbers posted are true, then thelikelihood of any applicant getting IW call is about 20 to 25% (
ratio of expected calls to number of applicants).
How much extra weight will the applicants with above 700 GMAT score be given, that will modify the likelihood of being called for IW; will it increase to 30% or 50% or 70% or only marginally is simply a matter of importance given to GMAT; similarly to what extent the likelihood of those below 700 GMAT score being called will decrease below the average 20-25% is once again predicated on the importance given GMAT score.
One thing can be told with reasonable degree of certainity that the likelihood of those applicants with less than 700 GMAT score will be less than the average (20-25%) and for those with 700+ score it will be more than the average, but how much less or how much more respectively is simply blind speculation

The likelihood of a particular applicant being called will depend on also other factors like your experience,career progression, essays, academic performance, ease of employability post- PGPEX etc.
All the best for every one