Whoever said the thing about differing geometry made a good point. Geometry translates to the ride pretty directly. At this level, the differences between 520 and 631 are negligible.

And as for everyone else who mentioned the "colorways" and how the bikes look...well, it's SSFG so I guess it's a pretty good point too. I want my bike to look hella pretty when I'm walking it up the 9% grade that I can't climb.