the multimedia library (many musics, many photos, many ebooks) requiert you have a quick memory card because there are many applications (from sony and google music by example) which are constantly read and resync, and check, and list the multimedia library content.
each time you take a photo, there is a process which re-read the entire library to rebuild an index.
Same thing with music, video content, there is always a process which need to QUICK read your memory card.
if your memory card is slow or not quick enough (like my sandisk ultra 64GB microsd XC I), then the entire device will slow that make you think it is obsolete whereas it is only a matter a memorycard speed and capacity (i have more than 6000 songs on my card and the process who read the art cover is very slow).
Each process who need to make a thumbnail of music or video or photo gallery need a quick memory card.
so you need to get a very quick memory card if you have a big library content (musics+photos+videos+ebook).
i have a slow (a not enought quick) microsodt card, so each time i took a photo, my device is slowdown because it rebuild the index of the library. there is the same bug with add mp3 song or video because the system took a huge cpu&memory ressource and time to rebuild the index of your multiemdia library.
making a index (video gallery or music album art ) NEED a quick card (and also a quic kcpu device but the Z3 own a quick CPU).
so do not under-estimate the speed you need, take the higher quick you can with your money (only if you have a big library of content).
As my experience, a sandisk ultra 64GB microsd XC I (class 10 i guess), is a bad speed for large library.
