Primary Progressive, from what my neurologist has explained to me is a pattern of progression, more than a speed of progression. In primary progressive, usually the symptoms gradually increase, with no, or few flair ups.

My course is similar, but slightly different. I have a form of progressive known as PRMS, which is similar to PPMS, with flair ups that I usually never completely recover from. When I first was told this, the speed of the progression was very frightening to me as well, as I didn't know what the future held. With mine, I have noticed that sometimes I will progress quickly for a period of time, then the progression will slow down for awhile.

I think the speed is different for everyone, and usually progression for males is faster than for females. That is just what I've gathered from chatting online to others with ms.