I am tryring to orchestrate my score for the musical theater. I can only have a very small string section (5 players, not including the string bass). The setting is the late 19th century to early 20th. So, I don't want to use electronic instruments (though, practically speaking, the strings will have to be amplified). I don't want to pad them with a synth.
Originally, I scored it for three violins and two cellos. Most often, I have them in a two way divisi (violins in unison, cellos in unison playing in contrary motion or an ostinato) or in sustained triads (upper voice = violins in unison, middle voice = first cello solo, bottom voice = second cello solo). For passages where the strings are playing solo or with light accompaniment (for example, harp + flute or oboe) I sometimes have the violins in a 3-way divisi and have one of the cellos play the bass.
As the score evolves, I am finding that I frequently need to have one of the cellos playing in its highest register (on the treble staff, up to the second D above middle C). It occured to me that it would make a better viola part. (For the times when I formerly used both cellos in unison, I could double the viola part with the cello or with the string bass, bowed.)
I have read that in a string section of this size, in a three way divisi, the minimum number of instruments should be 3 violins, 2 violas and 1 cello. The problem is that would mean I need another string player -- and the score would suffer worse by reducing the number of players in any other section.
So, my question is this: Is it better to go with 3 violins, 1 viola and 1 cello ... or to stick with 3 violins and 2 cellos (and let one of the cellos play mostly in its high register)?