Well that's a good improvement. Beware that if you're getting different timings, perhaps your MP3 player is fragmented (format should have fixed that) or your computer is too busy doing something else while transferring it.
For example, if you're transferring files to an external HDD and files to your MP3 player, its going to bottleneck. I don't know if you're doing something like that or not, but it could cause slowdowns.
Hope it gets better!