[V8i SS2] MS_FORCE_SOFTWARE_RENDERING / QV_D3DVERSION=0 Difference?

I am working on troubleshooting some issues and out of curiosity wondering...

What is the technical or practical difference between setting MS_FORCE_SOFTWARE_RENDERING=1 vs QV_D3DVERSION=0?

The goal is to force V8i SS2 (08.11.07.443) to "Software Graphics" of course, and both of the above appear to accomplish that.
But is there any difference for curiosity sake?

Thanks,
-G-