Comparing cells of two Worksheets

With the following Code I try to compare the content of two Worksheets.
The first column contains a key that is unique and the following columns contain data that I want to compare (My data sets contain around 7000 rows and up to 40 columns).

My question is if there is a way to make the code run faster. Since the program has to find the key first, it takes longer and longer the further down the row with the key is on the worksheet. A second thing I noticed is that the code generally runs a lot faster with Excel 2007 than 2013. Any ideas why?

Count = 1
LastRowNew= Sheets("Data_new").Cells(Rows.Count, "A").End(xlUp).Row
LastRowOld = Sheets("Data_old").Cells(Rows.Count, "A").End(xlUp).Row
LastColumn = Sheets("Data_old").UsedRange.Columns.Count
For i = 1 To LastRowOld
Set rngA = Sheets("Data_new").Range(Sheets("Data_new").Cells(1, 1), Sheets("Data_new").Cells(LastRowNew, 1)).Find(Sheets("Data_old").Cells(i, 1), lookat:=xlWhole)
If Not rngA Is Nothing Then
    Count = Count + 1
    Sheets("Comparison").Cells(Count, 1).Value = Sheets("Data_old").Cells(i, 1)
    For j = 2 To LastColumn
        If Sheets("Data_old").Cells(i, j).Value <> Sheets("Data_new").Cells(rngA.Row, j).Value Then
            Sheets("Comparison").Cells(Count, j).Value = "NOK"
        Else
            Sheets("Comparison").Cells(Count, j).Value = "OK"
        End If
    Next j
Else
    Count = Count + 1
    Sheets("Comparison").Cells(Count, 1).Value = Sheets("Data_old").Cells(i, 1)
    Sheets("Comparison").Cells(Count, 2).Value = "Doesn't exist in old system"
End If
Application.StatusBar = "Comparing entries " & Format(i / LastRowOld, "0 %") & "..."
Next i

The short answer is don't use VBA at all. Use native Excel formulas. We like to code, so it's natural that we all too often reach for the IDE when we should be heading to the formula bar.

Consider sheet Data_new

And sheet Data_old

You can use a VLookup from Data_old to find the corresponding values in DataNew.

=VLOOKUP(Data_new!$A2,Data_new!$A:$B,2,FALSE)

And then wrap the lookup in an IF formula to populate the final result.

=IF(B2 = VLOOKUP(Data_new!$A2,Data_new!$A:$B,2,FALSE),"OK","NOK")

resulting in the new & improved sheet Data_old.

StackExchange Code Review Q#86886, answer score: 2