I'm sorry that trick isn't working for you. As you mention LKML causes slowdown, it's possible that you're getting an inordinate amount of mail. It's also possible you've got an agressive IMAP client that isn't using one of those auth tokens (another common slowdown cause).
As I mentioned in a comment below* if this persists please to post on the help forums. There are people dedicated to helping there, and if it's a legitimate bug the backend team investigates and we fix the issues.
Hope that helps,
-Andrew
But if I try subscribing to LKML for a few weeks, gmail becomes completely unusable.