What is the best way to parse large XML (size of 1GB) in C#?
XmlDocument is not feasible in this scenario as it will attempt to suck that gigabyte into main memory. I'm surprised that you're finding XmlTextReader to be too slow. Have you tried something like the following?
using (XmlTextReader rdr = new XmlTextReader("MyBigFile.txt")){ // use rdr to advance through the document.}