On my 2007 Mac Pro (dual Xeon 2.66GHz) with Snow Leopard 10.6.3, Cubase 5.1.1, I have the 64-bit VE Pro server running, hosting one instance loaded with about 20+ matrices from VSL SE + Plus/Extended. There are no effects running in VE Pro, just the VSL SE instruments. I have 4 busses, as well, with 5-6 instruments going to each bus. At that point, VE Pro uses about 15% of my CPU when idling. (what the heck is it doing?)
When I connect to it from an instance of the VST3 plugin (two MIDI ports used to get at all the instruments), the CPU usage jumps to about 70% when idle. (what the @$%*!$ is it doing? :-)