Can someone help me write a macro that will concatenate across several columns and then find and delete duplicates. I can do this manually and it works very well; however, my spreadsheet has grown to nearly 20,000 rows so dragging the function down the sheet is very inefficient.

Here is my current workflow:
1) Create a column at the end (Row I) and name it Dupes.
2) Insert Concatenate formula into first row: =A2&B2&C2&D2&E2&F2
3) Click and drag formula to last row
4) Highlight duplicate rows by using conditional formatting
5) Copy duplicate rows to new sheet (just in case, I need to see what will be deleted)
5) Delete duplicate rows

Any help or guidance would be appreciated. I am using Excel for Mac 2011.