[pkautzsch]

Don't worry about converters' differences as to phase. As to sound: yes, do wonder, and use the best converters you have.
I'd suggest just a spaced pair, if it's choir only. Good room: omni, bad room: cardioid, and there you go. You might add wider spaced outriggers for a sense of fullness and more room, if the room is good.

The reason for the Decca tree's center mic being a few feet in front of L/R is that an orchestra's center section is a few feet back into the stage. So basically the three mics are equally far away from "their" part of the orchestra. Such a setup wouldn't really work out for a typical choir standing in straight rows.