DDR3 RAM should only consume about 4 Watts per stick. So, it’s not the power supply.
Does the crash lock up the entire OS or just Cubase? If it’s just Cubase, and you can still manipulate OS X around it, then it’s unlikely to be hardware related.
While some DAWs cough Studio One cough have had crashing issues as projects get large and consume more RAM, Cubase has been pretty good about this.
It’s probably just an ill-behaving 3rd party plugin. Remove them from the project one-by-one until you get stability and find the culprit.
Also, it’s probably not related to the buffer size, or CPU utilization.
If you noticed it with Waves plugins, and were on a PC, it could be video driver related, as Waves use OpenGL extensively, but on a Mac the video drivers are controlled by Apple and this would be less likely.
Do the prefs trashing thing, or boot Cubase into its safe-start mode (hold CMD+SHIFT+ALT and launch it).