David Warner becomes the 5th highest run scorer in Test matches as an opener. The highest run scorer as an opener in Test cricket is Alastair Cook scored 11845 runs and the second highest is by Sunil Gavaskar, who scored 9607 runs as an opener.
Most runs as an opener in Tests
11845 - Alastair Cook
9607 - Sunil Gavaskar
9030 - Graeme Smith
8625 - Matthew Hayden
8208 - David Warner