Hey, no problem - without clear documentation or a crystal ball we have to rely on socializing the information and that's tough enough, but even tougher with tech.
This short thread may be interesting:
http://androidforums.com/htc-evo-4g/135730-gmail-still-not-syncing-reliably-evo.html
Talk isn't canonically required for GMail - but the idea is that whatever service it coordinates is correlated to the sync delay problem for others.
Try it for a while with Talk off. Your 10 second result may indicate that there's more to the story or it may have been a coincidental result. Retest from time to time, or just go in every so often and see how the notification time matches up with the mail time. You can't say what was happening before, because you didn't know that Talk had run and set up this mysterious port/service, if true.
And - we've no idea that it might be the same or different with 2.2 - as that thread mentions, a single socket was all that was required.
Others with different custom roms report no talk/mail correlation and that makes sense to me - if all you need is a single socket, you'd think GMail would just deal with that all on its own.
Anyway, the other thread is short and gives food for thought.
Like you said, I don't have all the answers - that goes without saying.
- cheers, compadre!!
