Video here: /www.instagram.com/p/BvNiPafDxEW/.
There’s a reason why you see people wearing belts, and wrist wraps, and knee sleeves, and so on, when they go after big weight. The uninitiated and novice may call it cheating, not understanding that some of it is simply prudent planning. Think ankles in basketball, wrists in boxing, etc. Even for pressing here, a belt increases tension through the torso with an obvious increased effect of contractility.
Generally, I’m an advocate for as little support as possible with as full a range of motion as is reasonable. But when we combine various factors, the load can be immense: the extreme decline affords a great way to call upon an integrated effort from lats and pec, which can equate to a 1.5 to 2x heavier load than flat bench on decline, depending on the modality. The bridged decline invokes the hip extension tension much more thoroughly than an anchored decline bench. The belt increases tension. The slingshot keeps compression in the axilla. I have long had unnaturally strong triceps and lats; so I can go substantially heavier than a strict flat press where the pec is stressed more. For a lot of people, this is a way to put the pressing structures under much greater load for that much greater stimulus.
What did I miss? Wrists. My friggin wrists held up ok. But just ok. Barely ok. The right is a little... flared. For years I scoffed at guys wrapping wrists for any press beyond 300lbs, while I routinely went well beyond that. The kicker is always that muscles themselves can be ready to produce a force which connective tissue won’t yet be prepared to handle for another 6-7 months. Keep that in mind. Whatever your newfound athletic capacity, recall that certain structures in the body are not yet going to be ready for that for another 6-7 months. Powerlifters often discover this with the bicep and hands. Olympic lifters discover it in the shoulder complex. Larger muscle groups progress rather rapidly in comparison to smaller structures and the low oxygenated/low blood flow tissue like ligaments and even the tendons themselves.
Whatever muscles you have today, remember, you still have the ligaments of your 7-month-ago-self.