When I was experimenting with my RAMdisk that was an actual SATA drive the calculations I came up with for my 4c/8t machine to be able to do all CEP2 from RAM was going to be in excess of 32GB of RAM. Of course, that instantly puts you into the high-end (read: expensive) CPUs and RAM sticks, which makes it a non-starter too. To do less meant CEP2 work units would terminate and you'd get no credit. For me, if memory serves me right, the WUs will slowly take more and more RAM. Do note that RAm that is listed as "free" is in indicator, but they can still terminate with several GB of RAM available depending on your settings and such.

Definitely don't let me discourage you. Things cound have changed for CEP2 WUs in the last couple of years and I may be in error too. I just remember my system with 4c/8t and 32GB of RAM wouldn't cut it.