Will it sync with EM Client Tasks and Calendar
Todoist can sync with Google Calendar through an iCal feed URL, which means if EM Client syncs with Google Calendar, that will work.
We do not do anything directly with Gmail, except a special link is shown in our browser extension when an email is open. In this case, no it will not sync with the EM Client.
Feel free to add this as a suggestion in our votebox: http://todoist.com/Vote/
+1 (em Client with Windows8.1)