Query for games where the difference of player ratings was big I want  to run a query on a chess games collection which would give me games played by strong players vs weak players, let's say games from the first round of Open tournaments (Swiss system) where grandmasters face amateurs, so basically a query for games where rating difference is bigger than x.

What tools would you suggest? what method?
If you have access to a Chess Query Language tool you can use that, albeit I'm not familiar with it. SCID is free and more easily available : http://scid.sourceforge.net/

1)Open your pgn file 

2)Search header rating differences white - black = 200 - 40000