Concerning stability: use the tested&supported EmCORE r859 (Run UMSBoot from EmCore menu, connect to pc, copy the .ubi file to the 64MB drive, safely eject) in combination with a new daily build (just copy the .rockbox folder to your drive). To me, the behaviour you describe (data abort etc.) seems to come from too much undervolt in that custom build. Inconsistent performance of the database will probably fixed by this as well.
USB mode is difficult because of hardware encryption (if I'm correct), the workaround for now is to hold any key (MENU for example) while connecting the charger to keep playing music while charging the battery.
Edit: after a year of silence, now theseven seems to be working on EmCore, it seems with a focus on USB performance. Interesting!
Edited by r100 - 8/8/13 at 2:19pm