Razor, Spyderco puts out quality stones. If you had purchased the med. stone then the fine, I would have said, no you don't need the ultra fine. Because the company CEO posted on here, when ask about the ultra fine.
That is was the fine stone only sanded/ finished finer. Hence, I purchase the fine 2X8" stone and lapped one side finer. So, now I have one side fine and the other side ultra fine. Now, all I need is the medium. Since, you have the stones at the two ends, I have to say its a long jump between them. Better get the fine as well. I only got mine for my straight razor as I don't take my knives that fine. DM