From someone who has both the G56 & NV5600, I believe the G56 would be the better choice. After driving my G56 all week and then drive the NV5600 on the weekends, it reminds me why I almost bought the new Aison auto. The NV5600 is a HD trany and is the stiffest trany I have ever drivin, I actually formed calluses when I was driving it every day. The G56 has performed better than I expected and is a smooth shifting transmission and is more forgiving rowing through the gears.
The NV5600 needs more concentration, if you dont keep your mind on the gear your in, then 5th is hard to find and you have too double clutch and when towing can be a problem when you lose track of your gear and dont have your radio up too loud when learning shift patterns.
The G56 has issues as well, for example, 2nd gear is slightly taller than the NV5600 and when engaging the clutch in 2nd from a start, you must push on the throttle before it engages or it will stall sometimes, so I just start in 1st to prevent premature clutch wear. When accelerating in 4th and you are close to top speed and you shift to 5th you are already half way through the power band for 5th gear and you allmost feel like you slipped the clutch for a split second