Should we have a 3rd?

My husband and I already have 2 daughters, 12 & 6. I am almost 35, which we had always planned to be the cut-off for us. We're trying to decide whether or not to try for a 3rd or stop.
The age differences between ours are big. What does everyone think? We flip flop on this constantly. Our life is 'easy' now, with ours being in school. Does anyone have 3 spaced apart?