About the long delay in saving, I remember other people having problems when running KS from a USB (pen)drive; in that case, maybe it's the way the GZip compressor works, that it's unoptimized for USB. The general lag is however perplexing: it could be that each time the editor window is redrawn (blinking cursor, tile dragging etc.) the program reads from the USB drive, which slows things down considerably, but that's highly improbable.
I might try it myself later.