1858rem-
A few things that get confusing.
The New Model Blackhawk was introduced in 1973. It's not really "new", just newer than the Blackhawk which had been around since the early 1950s. The frame is the big, strong frame also used for the Super Blackhawk .44 Magnum. The "New Model" has a transfer bar and is loaded without raising the hammer, whereas the "Old Model" had Colt-style notches and a hammer-mounted firing pin. The size and weight, when Ruger made the switch, were the same.
The New Vaquero was introduced a few years back, to answer complaints from cowboy action shooters who found the original Vaquero (fixed-sight New Model Blackhawk really) to be larger and heavier than they wanted. So, Ruger brought out a gun that was about the size, shape and balance of the Colt Single Action Army (aka 1873). They also went to Colt-style one-handed grips, smaller and closer to the trigger than New Model Blackhawk grips.
Now along about that time, the Blackhawk hit its 50th anniversary, so Ruger used the New Vaquero frame to build a Blackhawk "flattop" that looks like the earliest Blackhawks in the early 1950s. They were smaller than the Blackhawks made since then. These also have the smaller grips, which Ruger calls "XR3".
The "50th Anniversary Blackhawk" is NOT the "New Model." It's either the "flattop reissue" or the "50th anniversary" or the "5/6 frame size" I think. The New Model is the one that's been around, essentially unchanged, for 36 years.
Both the New Vaquero and the 50th Anniversary Blackhawk are lighter and weaker than the New Model and Super Blackhawks. They appeal to those who don't need to shoot the hottest loads, but prefer a lighter gun with a one-handed Colt SAA/1851 Navy grip frame.
I prefer the regular Blackhawk and the Super Blackhawk. The grip sizes and designs were an outgrowth of Bill Ruger's friendship with Elmer Keith. If there was anyone in history who REALLY knew single-action revolvers for heavier loads, it was Elmer Keith.
Oh, and the Ruger Bisley grip really bears a lot of (okay, near 100%) resemblance to Elmer Keith's design "The Last Word" from the last 1920s, not to the Colt Bisley. Keith put a Colt Bisley backstrap and a plowhandle front strap/trigger guard on a Colt, and fit wood to it. There's an example in the Keith museum here.
Make sense?