encoders

Hi all!
I have, for a few years now, an iPod-Nano-2GB, used to ear music (and radio, with the hardware plug-in).
The musics in it where synchronized through iTunes, using all the default options.
Few weeks ago I received an iPod-Touch-32GB, and since then, I'm thinking about the best ways to feed and use all of them: Touch, Nano and iTunes.
If, by any chance, you have similar environment, please let me now how do you use it.

Now, for more specific questions.
I have around 500 CDs and decided to upload them to my PC HD, using iTunes. I intend, from times to times, move a subset of musics to Nano e/or Touch.
I made a single test with a few encoders and come to following figures.

I used, as source, a music CD with 772MB recorded.
a) iTunes, AAC-HighQuality, 128kbps, 44.100kHz (.m4a) --> 71.4MB
b) iTunes, AAC-iTunesPlus, 256kbps (VBR), 44.100kHZ (.m4a) --> 161.0MB
c) iTunes, MP3-GoodQuality, 120kbps, 44.100kHZ (.mp3) --> 70.0MB
d) iTunes, MP3-HighQuality, 160kbps, 44.100kHZ (.mp3) --> 87.5MB
e) iTunes, MP3-HigherQuality, 192kbps, 44.100kHz (.mp3) --> 194MB
f) Nero, HE-AAC, 65-74kbps (varies with the files), 22.050kHz (.mp4) --> 35.9MB
Other iTunes and Nero options come to very large files and where discarded. The Windows Media Audio option in Nero hungs up my PC (WinXP-SP3).

I conducted a series of listenings with all the above options, in order to decide which one sounds best for me.
Those listenings where made using iTunes plus a noise cancelling headphone, the Nano with the same n.c. headphone, and the Nano with their original earphones.
Well, after various reruns, I came to AAC-iTunesPlus in first, HE-AAC in second, and all other in third, with *minimal* diferences between all of them.
So, using storage space as the second factor of decision, I'm extremely inclined to go to the "HE-AAC".

Because 500 CDs will take a lot of time to upload, I'll really appreciate comments on above conclusions.
Any other suggestions (other encoders, other tests avaliations, etc) will be very much appreciated!

One final remark: iTunes plays the ".mp4" files but does not sync them to the Nano. I read in Wikipedia that ".m4a" are MP4 files simply with a different extension name used by Apple, so I changed the ".mp4" extension to ".m4a", iTunes sync'd them, and Nano played them very well! But, a little problem arouse: the playing time, showed by iTunes, aproximately doubles! Does somebody knows how/where to alter that kind of data?

Any comments/suggestions will be very much appreciated! Thanks in advance!
Regards, Ricardo