It does get a little quieter when you slow it down but mine makes a different noise when it's slow. It's not unpleasant but it's just a different frequency noise. But I bet it's only about 25% quieter at the most. I'll try to measure that sometime soon and report back.

As far as what you can print, that's all in the nozzles as you know. As long as you can hitch the nozzle to the X Axis bed and set it up in RAMPS/Marlin you can use it. I want to print nylon too but from what I've read about it, it's not the physical printers that make it difficult, it's just difficult. Sticking it down is a problem because it's a self lubricating kind of plastic. You don't have to cool it like PLA though, at least from the few articles I've read. There aren't many suppliers for filament yet either they said. However, I'm watching it as I'm sure I'll be retrofitting my i3 to experiment with nylon later this year. I'm too curious. Maybe we can start a "sticky" here that's about Nylon.

When you are talking about availability of nozzles, if you are referring to Makerfarm not having them then that doesn't mean there aren't other nozzles available. I just think Makerfarm sells what they like and what they know about. There are plenty of other places to get parts and add-ons that will work great with the Prusa i3.