Warning: I am writing what follows from memory because I have not had an MCM WU for days, so it will need to be checked when distribution of this project resumes.

What an MCM task writes into the BOINC directory during execution is essentially checkpoint files, i.e. a few very small checkpoint control files and a big checkpoint data file. The size of the latter grows with every checkpoint up to about 40 MB for an average WU (needs to be checked).

Knowing that there are at least 10 minutes between checkpoints for this MCM project (software coded) that gives a maximum 100 MB per hour per core, i.e. a very low load on the storage unit, whether it is an SSD or a HD one, especially since writing big files at once is the least stressing way of putting MBs on a storage device.

Also, note that if less frequent checkpoints are not a problem for you you can decrease the storage load for MCM tasks by simply increasing the Write-to-Disk parameter in your preferences.

Now the choice is yours...

You should be fine. I've got 13 years of crunching on a six core rig running at 3.3Ghz. Including CEP2, it is worked flawlessly on the SSD which was the cheapest one I could find at the time (Spring 2011).