On average Sobers took over two wickets per test, while Kallis took an average of 1.75 wickets per test. Both were outstanding batsmen, and enough has been written about their similarities and also their differences, in style and output as all-rounders.
Both Sobers and Kallis would have played for their respective national XIs as pure batsmen without a doubt. I hold the opinion that if they weren't great batmen, both would have played a significant amount of tests as bowlers anyway.
So the discussion here is about the greatest batting all-rounders beside these two. By definition, a batting all-rounder should bat in the top six the majority of the time, and take 1.5 wickets or more per test.