Re: what does nut material affect?
UI use graphite powder (the kind locksmiths use) on my nut slots to prevent sticking. Works great. I used to have all kinds of tuning problems with those unexpected "pings" when the strings slipped. Like most guys, I blamed the tuners & bought some replacements, but once I started lubing the nuts, I haven't had to replace tuners again. Much cheaper this way.
By using graphite powder, I pretty much get the benefits of having a graphite nut. You can't solve a problem much easier & cheaper than that.