1.75ct Morganite (Oval, 10.4×6.93mm, Light Purple) vs 1.75ct Aquamarine (Oval, 10.4×6.93mm, Light Blue)

All things being equal, Morganite will face-up slightly smaller than Aquamarine for a given carat weight, because it has higher specific gravity (2.8 vs. 2.72 - this means it's "slightly heavier" compared to Aquamarine of the same size).i Face-up size also depends heavily on the proportions of the cut.

Face-up area is a measure of the size of the gem when viewed from above (as set in a ring). It tells you how big the gem is at the girdle plane.