I don't know a shortcut to get to the last page. When I've cleared mailboxes at gmail, 100 at a go was good enough. I rarely use gmail as my reader. A cronjob grabs the messages each 10 minutes using fetchmail, and my gmail inbox accumlates at most a few messages in that interval.
I have 50 pages and over 2000 emails. Guess I should get started. lol