在C＃中使用自定义分隔符和一些非常非常大的字段值解析文本的最快方法是什么？

I've been trying to deal with some delimited text files that have non standard delimiters (not comma/quote or tab delimited). The delimiters are random ASCII characters that don't show up often between the delimiters. After searching around, I've seem to have only found no solutions in .NET will suit my needs and the custom libraries that people have written for this seem to have some flaws when it comes to gigantic input (4GB file with some field values having very easily several million characters). I've been trying to deal with some delimited te