Sd-1 4.0a vs 4.0b vs 4.0c

I am now the owner of Don Mason's Sd-1. I didn't pay attention when operating systems were discussed because I was playing a Yamaha Tyros then. My Sd-1 is using operating system 4.0a. Do I want to change this? If so to what?

Thanks,

Tom

Tom,
4.0a (New sounds, new styles, new 4.0 OS).
4.0b (Option to have old/previous SD1 sounds with the new styles and new 4.0 OS)
4.0c (4.0b PLUS more polyphony and smaller issues resolved).

If 4.0a works well for you, keep it.

Thanks,

AJ