I do not know if you are still looking for study material; but, I passed my extra today, I have no idea what my score was, they did not tell me. I used
http://www.hamtestonline.com/ and a few online books. I recommend at least taking a look at this publication
http://www.arrl.org/files/file/Instructor%20resources/ExtraClassSylalbus2009jan-AD7FO.pdf I had studied electronic technology in a community college certificate program over 20 years ago. So, quite a bit of the material was a refresher. I would recommend checking with the local radio club and see if they ever run a class. While I was at the test they mentioned that they were preparing to start a series of classes for General and Extra.