Hey,
I am so sorry to here you are having these problems, my daughter was diagnosed in 2002 with MM and had the revascularization surgery done on the right side of her brain. She had headaches and other little symptoms every once and awhile until school started in 2006, she was in 4th grade at this time and started having more headaches and fainting spells at P.E. and recess, it was still hot outside so we thought this might have contributed to the fainting spells. She started having other symptoms and her NL did a Diamox Spect. It came back fine. Symtoms got better as the weather cooled down. Then one Sat. night the beginning of Jan. she started complaining a finger on her right hand was hurting and feeling funny. The next day it still was so the ped. on call said to call her NL on Monday. They did an MRI the next day and said the blood vessels on the left side and up the back were now (5 years later) affected.  But they wanted to do an MRI of her neck on Wed. cause they saw something else wrong. I will get back to that. Anyway through prayers (which I believe in 100%)her angiogram showed that the blood flow was fine and that the MM had not progressed.  Now back to the new problem they found. These MRIs showed that she also has a Chiari Malformation, Syrinx, and Basilar Invagination. She had the decompression surgery a couple of weeks later and after some post surgical problems she is still doing fine. She has resumed normal activities other then not having anything tight on her head that could restrict blood flow(MM) such as softball helmets and goggles. But we can deal with that. But when she does have headaches and aches and pains we are in the same boat as you with wondering is this from the MM or the Chiari or just the normal aches and pains that everybody gets. She actually goes tomorrow for her annual MRI and we will see the NL afterwards to go over the results. Sorry to rattle on,I think you are the first person I have found that has both MM and Chiari. I also go on www.asap.org for the Chiari in case you haven't found that website.
To answer your question though I think MM progresses differently for everyone. 
Have you had decompression surgery?
Good luck with your MM surgery.

Tina
Shelbi 13 yr old daughter MM, Chiari Malformation, Syrinx, Basilar Invagination