Merging two Excel sheets by matching on two columns
If no one offered a suggestion, I have found a way to handle this. This makes it blazing fast:

Sub Verify()
Dim c As Range, last3 As Long, last4 As Long, last5 As Long
Dim wt As Worksheet, ws As Worksheet, wc As Worksheet
Set wt = Sheets("Temp"): Set ws = Sheets("Source"): Set wc = Sheets("Combined")
Application.ScreenUpdating = False

last3 = wt.Cells(Rows.Count, 1).End(xlUp).Row
last4 = ws.Cells(Rows.Count, 1).End(xlUp).Row
last5 = wc.Cells(Rows.Count, 1).End(xlUp).Row

wc.Cells.ClearContents ' Clear Contents
wt.Range("G2").Resize(last3 - 1, 1).Formula = "=C2&amp;D2"
ws.Range("G2").Resize(last4 - 1, 1).Formula = "=C2&amp;D2"
ws.Range("H2").Resize(last4 - 1, 1).Formula = "=MATCH(G2,Temp!$G$2:$G$" &amp; last3 &amp; ",0)"

' Copy &amp; Format Headers
wt.Range("A1:E1").Copy wc.Range("A1")

' Copy All Data from Temp
wt.Range("A2:E" &amp; last3).Copy wc.Range("A2")

' Copy Selected Data from Source
    For Each c In ws.Range("H2:H" &amp; last4)
        If IsError(c) Then
          last5 = wc.Cells(Rows.Count, 1).End(xlUp).Row
    wc.Range("A" &amp; last5 + 1).Resize(1, 5).Value = ws.Range("A" &amp; c.Row).Resize(1, 5).Value
    End If
    Next c
' Clean temp Columns
Application.DisplayAlerts = False: wt.Columns("G").Delete: ws.Columns("G:H").Delete
Application.DisplayAlerts = True: Application.ScreenUpdating = True
End Sub