Cobra V surely makes Cobra IV look like a sad mistake. Better firepower, fastest of all Cobras, highest jump range and best internals of all of them, on cherry of top being SCO compatible.
That being said, Cobra IV was always kind of "trophy" of sort, with very rarely being used by anyone, as even at its relase, was already underpreforming, mainly beause of its extreme slow speed, wich causes most of ships outrun it with ease. Wich is main issue with mk. IV... surely it would be more popular, if it would boost to atleast 500-510 m/s, and hardly it would make it overpowered in any way.
But it does not make much sense to compare old ships to new ones... new ships supposed to be better than older ones in virtually every area, and Mk. V does that perfectly.