I highly recommend Onkyo 6-disk carousel changers. I haven't timed the disk swapping, but I've always thought it was pretty speedy.

Keep in mind that a swap from, say, disk 1 to disk 4 will take longer that a swap to a neighbor.

The ultimate solution, of course, would be to rip all your CDs to uncompressed WAV or AIFF files -- you'll need a large hard disk -- and then pipe all your music to the stereo from your computer. We're talking millisecond access times here!