As the comments suggest, there is no real maximum range between two pitches of the tone row.
This is because, more accurately stated, these are pitch classes, not just pitches. In other words, we are dealing with octave equivalence: if the next member of your tone row is a B, it can be a B in any octave. Thus, if you come from a C, this B could be a major seventh above it, a minor second below it, or any other B. In short, the octave equivalence makes these intervals largely moot.
As for the technical demands of vocalists and wind players, serial composers were pretty demanding. In the opening measures of the first movement of his Op. 21 Symphony, Webern asks one horn player to move a descending major fourteenth (a major seventh plus an octave), another horn player to move this same interval ascending, and then the clarinet to return to this interval in its descending form.
It seems that the intervallic demands you speak of are less the demands regarding intervallic leaps and more the demands of the ranges of the instruments themselves.