I purposely added massive populations to see how far I could "push" TG4 and my new build. I built a scene with the camera at x=0 and z=0. When I added the pops, I just but them at 0,0,0 so a majority would be out of camera view. And yes, it used vm with the ssd.
I normally wouldn't be that sloppy, but this was just a combination of testing and me making the mistake of not clipping the pops from the camera.
I've been building my scenes lately around 0,y,0 and it seems to be quite efficient with my workflow. First, I use World Machine to get the basic terrain. Then, instead of moving the camera, I move the heightfield shader. I try to not rotate the camera in x and z, but sometimes I must. I use macros in World Machine to rotate the terrain build so I can get close to the view I want before it gets to TG4.
Now I put in the foreground pops at o,y, o with camera clipping. If I want a dense grass pop out to 20m, I make it 40x40. Background pops obviously need to be positioned either by x,z or altitude/slope, or some combination of those parameters. Now instead of having to move the camera and all the populations, I can move the terrain and (usually) adjust the camera height. Or swap in a new or rotated heightfield.
Okay, as far as 64 GB of memory.... I can set TG4 to 3/4 of my cores, start a render, and then run Lightwave/3D-Coat, or other apps. So far TG4 has not crashed except when I pause a render (Matt mentioned this was a known problem.)