There are actually at least 113 different affixes that a Mempo can roll for that random roll. I couldn't find an exact list of every affix an ilevel 63 helm can roll, so I manually went through all the different affixes on Mempos on the AH to get ranges, and tied them to the corresponding affixes. Some I had to list as only 1 affix, as the ranges overlapped each other, but could actually end up being more than 113 affixes total.
So to get the 6% CC, it has to roll the top CC affix, then roll 6% out of 5-6% (5%, 5.5%, or 6%).
1 in 113 for CC, then 1 in 3 for perfect, so 1 in 339
For a perfect, any one of the main stats works, so no need to pick dex specifically. Int may be a bit less desired, as it can roll higher on other helms, but Mempo is by far the best helm for any class (at least IMO).
so 1 in 31 for perfect stat roll.
then 1 in 10 for perfect AR roll
1 in 3 for perfect life %
1 in 2 for perfect IAS
so, 339*31*10*3*2 = 639,540
1 in 639,540 Mempos will be perfect. If you want to only consider a dex one to be perfect, then its 1 in 1,891,620.
Of course, if someone wanted to be a real dick about "perfect" then you can include armor and you get 1 in 38,372,400 for perfect of any stat or 1 in 115,117,200 for dex.
I don't know why I want to do so much math tonight
