They both sound utterly real to me. The only difference is that the plug-in has the powerful Kompakt playback engine \"built-in\" and it uses 24 bits samples (vs 16 bit in Giga).
Your system is minimal (actually a little above minimal sys specs), so it will work. Don\'t play much more than that good old Dutch \"twee vinger systeem\" though and you\'ll do fine. (Translation: Polyphony may be an issue...).
These two products are produced by two different companies; the giga version is PMI and the Plug-In is EastWest, so we can\'t offer cross-grades.
The plug-in is very friendly priced and you can get a huge additional discount when you register the plug-in and buy a full version of NI KOMPAKT or Kontakt.