Observations using same headphones (will differ) and exact same tracks
1) the 5g is significantly louder than the 7g
When playing the same track on my 80ohm dt770 I can relatively easily listen at full volume, the sound seems weak and I feel they are not powering them sufficiently, on the 5g I estimate the volume is 20-30% higher.
My dt770 80ohm seem harder to drive than the d5000 and with the 7g I would prefer an amp, with the d5000 Both can drive them fine.
Note: comparison done with ipod software and no eq and no volume restrictions.
When i get some time I will do the same test with my other older ipod nano 2g and 3g, but suspect the 7g will be left behind from memory,
Will post more as I go along/ till I get bored!! Ay questions just ask.