I don\'t believe the performance between the programs is different. Just features as you described.
As for the effects, two people could have completely different opinions about the same effect - you just gotta hear it yourself. Unfortunately, that might be hard for you to do without the effects available to you.
You got the details correct on the differences between 96 and 160. The 96 comes with the coolest effect which is the lush reverb. In A\\B listening tests, it compared to quality \"hardware\" effects and uses much less CPU than any reverb plugin on the market.
As to converting Stero to Mono, You would need to convert the waves at this point. The instrument articulation feature that is part of the GigaStudio will speed this process up. You could save an instrument articulation and then export the waves and batch convert them to mono. Then import them into the GigaSampler and match the folder and name arrangments the instrument had and load the articulation file. You should have a matching Mono version, paramater for paramater. It also wouldn\'t hurt to email the wishlist (firstname.lastname@example.org) and the Northern sounds wishlist for this feature to be automatic in a future version.