Yeah I have completed one already and had similar numbers as yours. I suspect its more the size of the firmware that goes onto takes up a fair chunk and then the true memory value being maybe 10-20 GB less than advertised on most cards. I know that the 7th Generation can go higher than this though - Ebay is evidence of this. I saw one guy had made a 1TB version! See the picture LOL! Tarkan's page lists some compatibility details but not much. Basically my friend wants to do his 6.5 Gen 120gb version and I'm unsure whether it will work or be limited if that makes sense at all.