Searching values of range X in range Y
It's hard to beat the performance of standard Excel WorksheetFunctions.
This will find the matches.


  Range("M4:M6525").Formula = "=IF(ISNA(MATCH(J4,$K$4:$K$6525,0)),"""",INDEX($K$4:$K$6525,MATCH(J4,$K$4:$K$6525,0), 1))"


Then if you want to remove the formulae use this


  Range("M4:M6525").Value =Range("M4:M6525").Value