Sustain, as much as your effects can push it, is still based on your guitar. Putting as much delay and reverb on your effects, will still suck if your guitar suck.

To me, the 3 most important aspects of the guitar that effects Sustain is wood type, construction and pickups. Like my RR3 has way less sustain compared to the fatter Zakk Wylde LP..... RR3 uses a lighter wood, Glue-On neck and a passive pickup compared to the Mahogany, Set Neck, Active Pickup Les Paul.

What guitar are you using btw?

ZNR is The Zoom Noise Reduction......... Unless it's a VERY high gain setting, turn it off. I didn't use it at all on my GFX-5.