Looks like you've done some homework.
I assume you're using the same ISP for both?
Couple things you might try.
1. Increase the number of simultaneous connections past the default two connection limit.
Normally the tweak is used to increase download speed but Outlook uses the same internet settings.
To do so, open the reg and navigate to:
Look for the two DWORD values below in the right pane.
If you do not see them, create them exactly as typed. Give the first one (Per1_0Server) a value of 20 and the second (PerServer) a value of 10. Exit the reg and reboot.
2. Increase the "Server Timeout" settings in Outlook.
Tools>E-mail Accounts>View or Change Existing E-Mail Accouts>Your Account>Change Button>More Settings Button>Advanced Tab.
3. Temporarily disable any E-Mail scanning functions in your AV software to see if it may be interfering.