Re: the scrolling tracks - ever played a high refresh game on an old LCD monitor that lagged? It was pretty annoying, right? Well, same thing with the display on the CDJ. The engineers have worked dozens of iterations of the GUI and how it performs (including one of my original preferences, to have the encoder knob rotate through things in the opposite direction), and some sacrifices have to be made in order to accommodate others. This one happens to be for visual ease rather than trying to frustrate you with how long it takes.
With regards to the speed differences, there's plenty of factors at play in there...
is the USB stick / port rated 2.0 or 3.0?
what is the type / spec of the memory controller of the USB drive? (typically VERY hard to find out)
is the SD card in a reader connected via USB?
what is the controller chipset of the reader?
what is the class (speed) rating of the SD card?
what is the format of the device?
how was it formatted previously? (just a FAT wipe or did the device get zeroed?)
do you have any caching enabled on your OS?
- have you already filled the card / stick with rekordbox data? (is it having to read and update existing files or simply write new ones)