I am surprised you chose a cushion if size is what you are looking for. Most Cushions are cut deeper than round diamonds, so the same carat weight cushion will oftentimes look smaller than the round diamond. I love cushions, so not trying to dissuade you, just want to make sure "the biggest diamond possible" is specifically for a cushion. The last 1.7 carat you posted has close to the same face up size of a 1.2 carat round.