1. I don't really know as I don't have any Class 10 card to test on. However you should take note that 'classes' on SD card refer to writing speed, not reading speed which is what actually affect the loading speed. I am using a Class 6 card and it doesn't feel particularly slow in reading. Also note that even a Class 4 card should be more than fast enough for full wave (uncompressed) file playback. I do remember reading from erji.net that others has successfully used Class 10 SDXC card on HM901, but it depends on brand as well.
2. It takes slightly longer on first start up to load ( / scan) the library and you can see album being added on-the-fly. You can play those already scanned files without waiting for the scan to be completed. It will rescan the library on subsequent restart as well, but seems to only looking for change. So if you didn't update the SD card, the rescan will only take a few seconds (or tens of second, hard to say as I didn't time it) and you can still select / listen to music while it is scanning on the background.
3.A 64GB will have to be a SDXC card and I don't own any SDXC card for now. Again, reading speed isn't an issue on HM901 as I didn't detect any delay between selecting files and listening to them.
I just did a drain test playing 24-192 file with JH16 on a HM-901 with balanced card. It lasted for 7 hours, from full charge and self power-off.
I am using a Kingston 128G UHS-1 Class 10 SDXC, formatted in FAT32, but as ClieOS already pointed out, that speed relates more to writing...
Thanks for sharing, ClieOS & ironore. :)
Looks like the HM-901 has about the same if not slightly more battery than the DX100, which is still acceptable (at least to me).
And will remember on the card classes portion, always mix it up for read/write speeds. :(
Hope to see some reviews here soon. It's finally march and looking forward to the international launch soon.