look - in my opinion, any single stone over e 1.5 carats is getting a bit gaudy. Also, unless your fiance is one of those girls, dont get too hung up on the color/clarity. no one is going whip out a loupe to check.
. go to an independent jeweler, set a price range, and work with them. I had next to no money put aside for a ring, and honestly, I thought what I got her was smallish, but 5 years later, with all my friends who had money, and had been planning to get engaged, she still has one of the biggest rings in our group, and constantly gets complimented on it. I spent 3K for an appraised value of about 9500 if that helps. I think that had as much to do with the guy I went to as the ring i got.
AND REMEMBER, ITS ABOUT THE MARRIAGE, NOT THE WEDDING, NOT THE RING, NOT THE HONEYMOON!!!!
If any of those things comes into play and changes ANYTHING - do yourself a favor and RUN.