Large SQLite database?

Has anyone had first-hand experience of using a large (2-4GB or more) SQLite database as a backend to a web-based application? Is there a significant performance degradation as the database size grows?

Also, how does SQLite compare to something like PostgreSQL in a VPS environment where RAM and I/O are at a premium? I've been Googling for a couple of hours now but can't seem to find any reliable information.

I don't need all the extra features that other RDBMS's offer, (SQLite is good enough for me feature-wise), so the comparison I'm looking for is about performance and reliability.