Guide to select appropriate gears

I have Canon 7D and 400mm f5. 6 for now. I want to upgrade some good gears.
I have some confusion about the same

7D || or 6D
300mm f2.8 or 150-600mm F5-6.3 tamron

can some help me to understand the difference of any guidance will appreciate.

what do you like to shoot? 6D is a very slow camera and its AF is quite poor when it comes to moving subjects. it's mainly a landscape camera.

thanks sir, mostly i shoot birds only, occasionally i do night photography and landscape.

i thought about 1dx. but i have some buget issue.

7d II with 300mm f2.8
7d II with 500mm f4

or suggest any good combinaton

Since you photograph mainly birds the 7D2 is a no-brainer. You mention the 500mm f/4 so I guess you have the budget for it, if so then that would be a better fit for "mainly birds". Either version is good, but version II is better. The seemingly soon to be announced 100-400 may be a good option, especially with a TC for extra reach when needed, if reviews are good when they start trickling in.