I will be heading up to North Dakota next month for a birding trip out on the prairie. Currently i have 7dii and 100-400ii. It would be nice to have a little more reach. Since i cannot afford to rent for 2 weeks or buy a Canon 600 was thinking maybe of renting the sigma or getting a Canon 1.4xiii to use with 100-400ii. For those that have used both would appreciate your thoughts. Contemporary or Sport? In the past i owned the old Sigma 150-600 (been a long time ago) and performance was ok, how does newer model stack up?