Something else to think about:
First gear is a decent amount lower in the G56 as compared to the NV5600. When driving my buddy's 07 with 3.73s and the G56 it was more like driving a 5 spd because you didn't use first gear at all. The NV5600 seems to be a 'better' 6 speed in that you hit all the gears because first gear isn't as low.
On the other hand, the G56 with 3.55s (if that's what is in your 2000) may be more suited to using first gear. (If you've got 4.10s, first gear won't be used a whole lot on the G56.)