Interesting article on the history of the memory limit. As can be seen, the memory limt for 64 bit Windows is recommended to be MIN(60%, 1TB).
http://blogs.msdn.com/tmarq/archive/2007/06/25/some-history-on-the-asp-net-cache-memory-limits.aspx
Jesper Jørgensen, www.sitecore.net
