I have an i7-2600K processor and 8GB RAM. Currently I use Inkscape r12605 build. I've found the multi-core setting, set it to 8, restarted program... And it changed nothing at all. The files I open render sluggishly, even if I hide blurred shapes. More than that, if I open the very same file in Inkscape 0.48.4, it renders a bit faster than in the r12605 build. That's odd.
I use Windows 7, btw. Not sure if it matters though.