Great comparison! I'll go for the SK. I hope you get the chance to compare the GX-7 with SK-7 in the future...I am considering upgrading to one of these down the road.
Both pianos sounded great to me. Your playing was very nice too Ted. The SK5 has a more crystalline upper register in my opinion. More bell-like and pure. But the GX5 is a really top level piano. If I was a professional pianist or a dedicated enthusiast with an extra thick wallet I might go for the Shigeru because I never heard one that didn't sound fantastic. Having said that, I could be absolutely content with the GX5 though.
It’s like a custom shop Gibson Les Paul vs a Gibson Les Paul standard. Both incredible instruments, but maybe the custom shop gets you that extra 1%. Fantastic playing, Ted.
At this price point you can just attribute the difference in sound do to the fact that they are different instruments. One of them is embellished with some extra features that dont necessarily make the instrument better in terms of sound. Simply put, at this price point both are amazing instruments and the deciding factor should be getting the instrument that sounds better and motivates you to play as much as possible.
SK is more clean, and if you play piano long enough, those vibrations, overtones and cleanliness rivals the Steinway, Fazioli and Bechstein. Sk is apparently is a much more expensive piano than the GX model.