Maybe that's just it -- with both "flash" and "style" we immediately think speed but when it comes right down to it, speed isn't the defining factor of either. Eye-catching and enjoyable would be better definitions.... So maybe momentum = perseverance?
To the first point, as much as many people attempt to diminish the role of speed in defining style, "speed" does not imply an amount. It is, however, a necessary component of a definition of style that gives a fair and comparative tool to judges in judging overall performance. Directly from the AKC rule book:
(7) Style is apparent in every movement of a dog and throughout his entire performance at trials, for example: by the gaiety of his manner in approaching the line, by his alertness on-line, by his eagerness and speed
on retrieves, by his water-entry, by his pick-up of birds and by his return with them. Style makes for a pleasing performance; together with ability to mark, they constitute the most important factors for placing’s in Derby Stakes.
In all stakes, in respect to “style,’’ a desired performance includes: (a) an alert and obedient attitude
, (b) a fast
-determined departure, both on land and into the water, (c) an aggressive search for the “fall,’’ (d) a prompt pick-up, and (e) a reasonably fast
return. Dogs may be credited for outstanding and brilliant exhibitions of style, or they may be penalized for deficiencies in style — the severity of the penalty ranging from a minor demerit, to elimination from the stake.
I think your "momentum = perserverance" idea has real merit. One of the dictionaries' better definitions of momentum includes "the ability to maintain velocity against resistance". Things like distance and terrain are factors that provide resistance, and a dog with strong momentum can maintain velocity in their presence.