7.62x40WT is nothing more than a slightly modified .300BLK. If you don't like blackout, the don't even look at the 7.62x40WT.
There is no cartridge that will fit in an AR-15 magazine that will ethically take a hog at 400yds. Hogs are tough. If you want a 400yd hog gun, get a AR-10 in .308win.
For an AR-15 good to 400yds on humans or whitetail deer, either the 6.8spc or the 6.5 Grendel are what you are looking at. I favor the 6.8spc as an alternative caliber, but nothing in the AR platform beats the 6.5grendel at extended ranges.
6.8spc was designed for a 14.5-16" barrel. Optimum SBR length is 12.5". 6.5 Grendel was designed for longer range and longer barrels 18"+ but it still performs out of a 16".
Also, nothing will be as quiet as a .300BLK suppressed, except maybe a 9mm or a .22lr
The only calibers from an AR-15 that I would be comfortable trying to make kills at 400yds would be either a 77gr 5.56, 6.5 Grendel, 6.8scp, or a supersonic .300BLK/7.62x40wt