Just to add a data point: I synced a "large" folder to my Tab Ultra and timed the ls operation. With roughly 7500 files, it came out at around 13 seconds:
Code:
BOOX:/ $ time ls -Rl sdcard/Documents/ | wc
7483 51281 464234
0m13.43s real 0m01.17s user 0m03.21s system