You can download a fully functional trial version and see for yourself.
For how I use NX, as a raw converter with images transferred to Photoshop
for finishing, I could see absolutely no advantage to the upgrade as what is
added is better done in Photoshop.
I use NX on dual core (AMD and Intel) and Intel Quad core machines, laptops
and desktops, and have never experienced any problems with speed or
stability. I used to use it on a Pentium 4 laptop without problems.
Rather than paying for NX2 it may be more worthwhile looking into the new
Nik plug-in (Nik is the actual source of NX) for Photoshop that does
essentially the same thing and possibly more.