It's my understanding that a "New Model Blackhawk" is a large frame single action with a fluted cylinder and a "New Model Super Blackhawk" is a large frame single action with an unfluted cylinder.
Once upon a time, that was true, today, not necessarily.
Ruger actually made the Blackhawk in .44 Magnum. In fact, they actually got their gun on the market a few months before S&W got the model 29 to dealers.
When Ruger introduced the Super Blackhawk, both guns were produced side by side for several years, then the .44 Blackhawk was dropped and all the .44 Mags were Super Blackhawks from then on.
And for decades the Super Blackhawk only came in one flavor the 7.5" barrel. There was a 10" version offered for a while, don't know if its still made.
According to the stories, Bill Ruger got concerned about the durablility of the .44 Blackhawks (gun life, NOT strength) and created the Super. The Super is heavier and so a bit more pleasant to shoot as well.
The differences between a New Model Blackhawk and a New Model Super Blackhawk are that the Super had an unfluted cylinder, the ejector rod housing is steel, the grip frame is the "dragoon" style and is steel (and slightly longer), the trigger is grooved, and the hammer has a slightly different profile, the spur being lower and having a wider thumb pad.
For may years, that was the only way a Super Blachawk came.
TODAY Ruger will sell you a SUPER BLACKHAWK with a fluted cylinder and a regular (round) style grip frame as well as the older style.
SO, today, you can get a Super Blackhawk that is visually virtually identical to the Blackhawk. And both are made on the large (44 size) frame.
Ruger has also "re-introduced" a Flattop frame, I do not know if it is the same as the old, original ones or if it has a larger frame.