Ring sizing

[beckkl]

I am looking at getting this ring for my girlfriend:

http://www.whiteflash.com/Engagement-Rings/Styles/3Stone/Pear-Shape-Side-Stones-by-Vatche_697.htm

I am wondering, will a 1ct center stone look too big or small on her size 4 finger? I''m hoping to find a balance. Also, if I decide to get a setting from one jeweler, and the center from another, how to I go about getting it "assembled"?

Thanks!