Previously, we've had the following size limits for all groups:
For premium and enterprise groups, I've raised the Photos and Files limits to 500MB. I've kept the max email size the same because many (all?) email service providers have limits on the size of emails they will accept. I don't have specifics, but my gut says the majority limit message sizes to something under 100MB.
(Photos and Files referring to uploaded photos to the Photos section and uploaded files to the Files section).
On the TODO list is work to better support better file/photo uploads, allowing for pausing and restarting transfers and dealing better with unreliable network connections. I don't have a timeframe on that, however.
Please let me know if you have any questions.