68000 tracks and 700gb?, What compression do you use, mp3 in 64 - 128 kbps?
I have about 10 000 tracks in a 250gb hardrive @ 320kbps but i leave 15-20% free because its SSD.
Another with flac and wave with less tracks due to the bigger sizes.
If the lists take long time to read (Load) it can depend of the size of the playlist you have.
Keep the small and manageable.
if you use a PC with a "traditional" harddrive, (NOT SSD) don't forget do defrag the drive from time to time.
Ive begun to notice problems with flahbased hardware and i make sure to keep my backups on different sources. Cause some day these flashdrives will crash!