I'm not sure what you mean. You didn't burn your nickel coil at 500°, nickel melts at 2651°F. Do you mean burned the wick? 400° shouldn't burn dry cotton. When it's wet you can go higher.
I think titanium burns at 1472°. If you did pop the nickel coil there was a different reason than temperature setting.
I don't think the VT is very exact with it's temperature but I do think it's consistent (you could search out a pbusardo review video to find out) so once you know what you like on that mod/liquid it shouldn't change much