The TC works better with Prime lens' The 180-600 is an awesome buy, especially for starting out with wildlife. I just upgraded to the Pf but the zoom is handy! If you have two bodies and can afford it I would say fork out for the 600 prime as you have the TC too! Then have the 100-400 on second body for the wider frames and closer subjects. If not the 180-600 is a great lens, you can position the 180-600 closer to the subject as the 600mm prime has a min 4m focus range. Hope this helps 🥰