.75 for a solitare isnt bad. it depends on the girl though, and what she wants. I have small hands, so i dont want anything big. My bestfriend on the other hand, has smaller hands than i do and has a huge ass ring that she wants to get a bigger center stone for.
It all comes down to what the girl likes. The size isnt as big of a factor as the other 3 C's. You can get a 2c diamond, but if it's yellow and has imperfections in it, it's going to look like shit..and no woman is going to care that they have a 2c diamond when it's looking like that.
Oh and, Bluenile > *.