Galaxy S3 stuck on boot loop, Factory Reset didn't work
I had same problem with logo loop.. I somehow screwed my EFS folder, but don't actually know how... Anyway I tried like 150 different thinks to fix it that I googled out but non of it worked for me.. 
Finaly I download orignal stock ROM but the old one with 4.0.4 android. Flashed via ODIN and only then get rid of logo loop and phone turned on normally (it took allmost 5 mins..) Then I restored my EFS folder. Than rooted the phone, installed CWM and made nandroid restore of my original ROM..
Not sure if this help, but saved my ass :) Wish you good luck