If it doesn't slow it down I might just use witch's tutorial to give buy, build, cas and neighbourhood the same soundtrack.
If you stay in any of these places long enough the music cycles to the next category anyway, once it plays through the first (at least since Nightlife).
Well I have put about 50 songs, some of them up to 7 minutes long and I haven't noticed any difference in the loading time of the game.
Heg, the file format was WMA but they didn't work in the game at all. I used to be able to change the file format (and still do on my old computer) from WMA to .mp3 in XP to upload songs to my mp3 player. It works just fine, so it is slightly disconcerting to hear it shouldn't
I'm guessing the files are being converted on-the-fly while being transferred.
Also, some portable music devices can play native WMA files.