I found this guy who made a tool for testing if you are able to pick up on small changes in input lag.

I suspect most ppl here will have no difficulty, but it will be interesting to see.

forum: http://forums.blurbusters.com/viewtopic.php?f=10&t=1134

(he has a link on forum, i uploaded elsewhere for convenience)
tool: http://speedy.sh/7WnTk/inputlag-AB.zip