"Go with the flow" ought to be inscribed at the top of every music score. Performers and conductors just get themselves in trouble when they buck the natural organic motion that good music defines for itself. Thus, Gerard Schwarz and his Mostly Mozart Festival Orchestra produced a splendidly energetic and idiomatic performance of the Bach E Major Violin Concerto at the last of the four Mostly Mozart Festival concerts at the Kennedy Center on Saturday but a reading of the Mozart A Major Piano Concerto, K. 488, that was more diligent than spacious and more resolute than sunny.

The difference was in the flow. Bach's music, with roots firmly anchored in a German idiom that, like the German language, moves with a strongly rhythmic and balanced cadence, needs to maintain the sort of drive that Schwarz excels in. Mozart, on the other hand, was much more Italianate in his discourse. His music moves to the more irregular shape of the rhythms of the Italian language and needs more flexibility than either Schwarz or pianist Alexander Toradze seemed inclined to provide.

Toradze is a bear of a man whose physique might lead one to expect bombast, but in fact he approached the keyboard with close care and concentration. His performance was safe and solid and profited from well-integrated collaboration with the orchestra.

Violinist Nadja Salerno-Sonnenberg was the soloist in the Bach. This is music that seems to suit her outgoing and action-loving spirit, and she played with a focus and drive that was, at the same time, daring and well controlled. She found a silken tone for the second movement adagio but superimposed on it a vibrato that was both too wide and too fast for the broad sweep of the lines.

The concert ended with the Mozart Symphony No. 41 ("Jupiter") in a big and powerful performance that looked ahead to Beethoven rather than sideways to classical restraint for its inspiration. While at times the inner voices seemed cataloged rather than revealed, the orchestra produced a fine palette of colors and of textures.

Pianist Anne-Marie McDermott again anchored the preconcert concert and may well be the unsung heroine of the festival. She began with a beautifully conceived performance of the Haydn E-flat Major Sonata, shaping the fading repeated notes motif of the finale with great control, and then teamed with Salerno-Sonnenberg for a decisive account of the Beethoven D Major Violin Sonata (Op. 12). The duo found a splendid variety of moods and personalities for the variations of the second movement, and moved from one to the next with subtlety and a fine sense of ensemble.