I have this measure in DAX in a Power BI report:

Code:
Count Over 75 =
    SUMX(
        SUMMARIZE(
            'FactTable',
            'Employee'[EmpID],
            'Employee'[StoreID],
            'Project'[Project],
            "_Over75", IF([MeasureOfInterest] >= 75, 1)
        ),
        [_Over75]
    )
It it working as expected. It returns the correct result at all three levels of drill-down (StoreID, Project, Employee) on a matrix visual.

The data source is an SSAS database.

What would an equivalent measure in MDX be? I am looking to create an MDX Calculated Measure that can be used in Excel. I have tried the below but it is so slow it times out the connection after 20 minutes!

Code:
SUM(
    EXISTING
    (
      [Employee].[EmpID],
      [Employee].[StoreID],
      [Project].[Project]
    )
  ,
  CASE
    WHEN [Measures].[MeasureOfInterest] >= 75 THEN 1
  END
)