The various trials in the 1950s were long before the XM9 trials in 1979-1980, and then again in 1984, so its apples and oranges. Beretta only had the Model 1951 at the time the 1950's trials, and I don't believe it was entered.
In regard to the XM-9 trials, the S&W 459 was the S&W entrant in those trials which were strictly limited to double action semi auto pistols.
That DA requirement disqualified what became the FN SFS Hi Power (bottom), even though it accomplished the same goal very elegantly, without separate DA and SA trigger pulls. They also entered a double action development of the Hi Power, what became the HP-DA (center), but it just wasn't successful.
The Browning BDM (Browing Dual Mode) (top) was developed later for the FBI trials and it also was not successful (personally, I think it just feels funny).
But... the original points in my posts are two fold:
- If the US Military had adopted a 9mm pistol in the 1950's it would have allowed a more modern 9mm pistol about 30 years sooner; and
- the Beretta adopted in the XM-9 was a poor fit for many troops.
The US Military would have been better served by issuing a development contract for a variant of the XM9 that incorporated better ergonomics, along the lines of the current Beretta 92X with thinner grips and a short reach trigger.