2x or sigma
If you can't spend $1500 for Sigma 50-500 OS don't waste your $$$ on 120-400 zoom its a junk. No 2X TC on that 80-200 will not work well but for about $450-550 you can get FX 400mm prime f5.6 that dose macro at 1:3 and its taking Kenko 1.4XTC well in good light it is Sigma APO macro one with 77mm filter. Its hard to get but it is better than all zooms in that range. Besides 50-500 OS.