I believe GMT900 smallest wheels are 17s, they don't go any smaller.
If you look at my previous post, you will see how much had to be removed with 17" wheels. You would still have to remove some even with 18" wheels too.
As far as how it handles, honestly I haven't really driven it much. I just got it aligned early this week and its out of spec. I need to replace my uppers with stock arms and then I'll be good.
From driving to and from work, it feels ok. Haven't really thrown it around any corners due to the alignment. An overall feel, it definitely feels better than before. But, I think I'm going to go with a coil-over conversion because I don't think its firm enough for my liking.