Voted 2.5ct as a happy medium. That will look plenty big on a size 4.25. You also might want enough room on your finger to see the side stones, otherwise, the center stone might hang over the baguettes, or the bench has to open a large enough space to accommodate the head, and then the sidestones end up unseen between your fingers.
"Lucky I'm In Love With My Best Friend" - 18 wonderful years on 11/13/11! I love my kids!