MPC 4000 and MPC 4000 plus... any difference??

I'm planning on buying my first MPC and going straight for the 4k, but I can't figure out anywhere if there is a difference between the MPC 4000 and 4000 Plus? Is there a difference? Is the 4K always referred to as the plus? Are the white ones regular and the blue ones plus?

As a side note, I was wondering how everyone felt about the reliability of a used unit? It seems to me that several units will have one or more pads not working or having a different velocity curve. Also, there are allegations of bugs plaguing the 4K. Was this just in earlier software revisions, or can I expect headaches if I buy a used 4K?

Thanks
-Jeremy

http://www.mpc-forums.com/viewtopic.php?f=24&t=89745

The only difference is the plus comes with the wordclock/spdif I/O and the standard 4k doesn't. The machines are still the same though.