Right now we're reasonably confident that we've tweaked enough stuff that even very large imports should succeed! Give it a try, and if it fails, let me know and I'll check to see if the failure was anything other than "blocked by LJ at that exact moment".

(To put "very large" into context: we have a comment import with 7 million comments in the queue right now and we're about, like, 85% sure it's going to work.)