In my honest opinion, I believe it is unlimited. Those hubber score should be also calculated along with participation level, activeness and even traffic. That is what I believe but I could be wrong though.
I think the number is not entirely relevant. When calculating hubber scores a lot of factors are taken into account. Publishing lots of average or below average hubs every day will bring your score down I think as the content is not great.
On the other hand not publishing that often; say once a month could be detrimental as you could be seen as not being active in the composition sections of Hub pages. If you publish at one every few days, and ensure they are good quality, and answer questions, leave thoughtful and insightful comments on other hubs i'm sure you hubber score will stay high.
I don't know since I only publish hubs when I can because my education comes first. But ask me again when I receive my Bachelor's Degreee next August and I can probably give you a better answer, that is, unless I go on toward my Master's, which I also plan to do. Just thinking of all the work I have before me sure makes this 54 year-old tired and sleepy, LOL.
Number of hubs is not that relevant. The hubber or profile score will rise and fall based on several factors with the main weight being the number of visitors that your hubs receive over a specific time frame, usually on a 24 hour cycle. Granted the more hubs the better your odds of receiving more visits.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.