my 2 cents:

1. do you go 32 or 64 bit OS?
   With 32 bit your user mem is limited to 3Gb (2Gb if you run Windows and don't adjust it). A scene plus each well dressed figure in it take about 500Mb in rendering so that puts a limit on your results - while as madno2 shows: there are exceptiong to this rule of thumb. Running Poser 9 or PoserPro 32 in a 64 bit OS presents you the same 3Gb limit. Only PoserPro 64 in a 64 bit OS takes the limits off. In that case, more physical RAM available prevents disk-swapping in very rich and crowded scenes.
   (I run win7-64 with 24Gb RAM)

2. do you render with Firefly or do you consider LuxRender or Octane?
   FireFly likes lost of CPU power but brings no videocard requirements, Octane requires a high-end nVidia (!) card with lots of CUDA's, LuxRender takes both videocard suppliers and mixes with CPU.
   (I run an overclocked i7-990 with 12 threads, and a basic nVidia 560. Will uprade to nVidia 780 or Titan for running Octane soon. Videocards are easier to upgrade later than CPU).

Note that LuxRender as well as Octane might take loads of RAM too while running.

3. SSD is typically a write-less-read-very-often device, and should NOT be used for temps etc. Do not defragment them either! I use my SSD for OS/Program Files and a Manuals cataloque (my 256Gb is only 40% utilized), my data is on a normal HD (6Tb in the casing, 12Tb external incl backup), so the SSD just speeds up program launches. As I run a say 1Tb Poser / Vue / ... Library, there is not much sense in assigning a SSD for that. Far too $$$
   I prefer loads of RAM (24Gb - my motherboard limit), and dedicate a portion of it (4Gb) to a RAM-disk which takes my temps - I reassigned the Windows TMP and TEMP settings - , and as a plus: it always comes up clean after reboot.

4. consider other programs you're running as well. Vue loves RAM but - except for xTreme - takes 8 threads max for rendering, and does not use GPU. Photoshop loves RAM too (and again: do not use your SSD for swamp/temp/workspace).

All the best.

- - - - - 

Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though