Justin, the power of Gigastudio - actually greater power than Giga 2 (the current version) - is in Emagic's EXS24. Kontak isn't as efficient, but the latest version is also very good. The only problem is that it's not practical to run EXS24 on multiple machines, and until we get 64-bit memory addressing, one machine isn't really enough to deal with large libraries (e.g. Vienna Symphonic Library).

Everyone's eagerly awaiting Giga 3.

However, Pro Tools isn't set up to deal with these large libraries, especially the orchestral ones. Briefly, the reason is that you need to have dozens of articulations loaded up and ready to try out for each phrase or even each note.

I'm not posting this to fuel the stale argument, just explaining that other samplers than MachFive are working very well.

By the way, the Access Virus Indigo plug-in for PT is awesome if you're looking for a software synth that won't eat up your CPU (since you have Pro Tools hardware).