One account has 2.5 GB, another has 700 MB. I'm on a lot of mailing lists and get a lot of transactional email. I just timed switching a label and that took 4s on the smaller account. This is in Chrome with SPDY enabled, too, so I doubt it's client transport.

I should probably note that it tends to be variable with the time of day. That's not unexpected, but still kinda sucks.