Might I also suggest too..........a 3/4 carat Princess cut is going to be HUGE unless your girl is like 6'4" and 300lbs!
I'd say go w/ a 3/4 carat at the MOST and you'll be plenty happy! (And so will she!)
You could even get her an .800 pointer & tell her how it's actually *bigger than* a 3/4 carat.
I recently did a 3-stone ring for my wife for our anniversary and put an approx .700 pointer in the center w/ 2 .330's (approx) on the sides and it came out beautiful. Actually kinda' makes the wedding ring I got her pale in comparison.
Anyway, all 3 stones are D/E and IF/VVS1. (Center stone is worth a LOT of money for its size).
When my wife strolls in the sun, that thing pops off like a strobe light & could seriously blind you. Lemme see if I still have pics here at work & you can see how beautiful smaller stones can be........(If you can call a .700 pointer *small*!)
Here's a pic I have from work before I gave it to her..............
Fire & Ice!!!!!!!!!!!!!!!!