The most popular diamond stud shape has been the round brilliant because people believed it to be an "ideal cut" that displayed the most brilliance and sparkle in a princess cut diamond.
While the weight of Tiffany Style Diamond is important, it doesnt necessarily provide the "perceived size" of princess cut diamond. A shallow cut diamond will have a greater diameter, and will therefore look larger.
a flawless diamond wedding ring is no more beautiful to the unaided human eye than a grade in the middle of the scale. Once again, extremely subtle differences in clarity are very important to determine rarity, but only affect beauty when in the very low end of the scale.