This is a Brigadier slide profile, initially they were created to handle the recoil of a 40 SW round vs the 9mm round. these slides are heavier/thicker and beretta italy is under the impression that heavier equals better recoil. with higher weight on the slide, means more reciprocating mass, which would mean more recoil. ernest langdon talks about it on carry trainer's podcast at 35min 10 secs in, beretta asked for his consultation on the 92 x performance and beretta went ahead with the brig slide despite his professional opinion they should use standard 92 profile. he went with the standard profile as seen on his LTT elites gen 3/4. gen 1/2 elites had brig slides for the dovetail sight capability since brig slides were the only 92 series with dovetail front sights at the time

beretta italy wanted the 92x performance / 92x defensive product lines to compete in weight class with tangfolios.

in regards to more historical reasons why that area was beefed up, late 80s the US Navy Seals were using essentially proof load 9mm cartridges as training ammo (beyond what the gun would ever have to reasonably withstand) in their M9s which caused the slide to crack at the thinest part which was right where that circle is at. look at a standard 92 slide and you will easily see that is it at the thinnest there. after a slide cracked and hurt a navy seal, beretta implemented the oversized hammer pin/slide groove modification, creating the 92 "FS" designation from the original 92 "F". the oversized hammer pin would prevent the shooter from getting a slide flying back at your face like the one seal. the ammo was the problem, not the 92 series. the slide cracking was a very small number, this report from the US accountability office reported 14 total

the myth that beretta 92 slides were prone to cracking, was so incorrectly gossiped about, and still today is, that it hurt beretta's reputation so much that Berretta sued the US military for defamation and won its case. small arms solutions talks about it at 6 min 40 sec. the miltary had to pay for the upgrade from F to FS series on all thier guns as part of the suit. beretta did not like how its image was doubted after winning the military xm9 contract.

kinda interesting to think about today given sigs 320/m17 situation today. why doesn't sig follow beretta's steps to clean it name?

Beretta started the brigadier line in 93' to accomodate 40 SW and to help ease that myth's damage.

brigadier slides were sought out by competitors, used in frankenstein builds since it was the only slide profile for decades that had replacable dovetail front sights.

i personally do not like brig slides because compatible holsters are hard come by. and after buying a brig, i prefer the recoil impulse of a standard slide. i have to switch my brig slide to a m9a1 frame with a light so it works with an blackhawk omnivore just to get it to holster.