So there are a few commercial cartridges that beat 4000fps, so this would mean at least 20000fps. For a 55 grain (pretty standard) bullet that would give us well over 48,000ftlbs of muzzle energy.
As for recoil I haven't a clue what the powder charge for a 55gr/20Kfps bullet would be but just throwing out 500gr charge for that bullet weight and velocity would be 13Kftlbs of recoil in an 8lb rifle.
Beyond the massive stupidity of making this claim in the first place is the galactically moronic idea that the exact same cartridge fired from one platform (a 5.56 in a bolt action) is somehow going to x5 the velocity out of an AR. It's an observation so eye wateringly absurd it would make a salad bar explode into laughter. Now contemplate how many people may have actually believed that nonsense.