Grand Piano for Gifted 6-Year-Old (Kawai GL or GX?)

I would hold off on a grand for a while.

I consider it most important that your current piano is perfectly tuned,  the keys properly weighted and a good overall tone.

Speak with your trusted tuner and if she/he considers the piano meets these needs, then hold off.

If not I'm afraid I can't advise on which model better (I have a Boston) but again I would put my trust in the opinion of a good tuner. 

The Yamaha Cx series is the better built piano with more resonance , more protection of sound and probably will last you a life time. It has more string length and more detail in the sound board. The new ones are almost as good as The Bosendorfer(which I have). This is a serious piano hence the  price. 

Since your daughter is only 5, she needs to play a lot more piano- to a more advance stage to know her mind. A piano is a very personal thing, like choosing a partner in marriage. You can’t choose it for her and she be stuck with it for all her youth growing up.  First of all, you need at least a C3X which is 6 ft. Or bigger to be worth while. No point in having anything smaller, ior else it will be the same length of strings as a full upright.  When she is older and knows her mind, She has to choose it for herself . If you insist on buying it now. Then you should take her teacher with you or someone who plays well to know the difference.  For most pianists, this is the purchase of a life time  The half life of a piano is about 30 years. There is nothing wrong with a full upright if the action and sound are fine. At present, her little fingers will not be able to make use of the power of a 6ft or bigger grand.  You should talk to her teacher about this.

I have had a Yamaha G3 and C3. I now have a Steinway Model B.  My students have Kawai GX, Shigeru-Kawai, rebuilt-Steinway, and Yamaha CX.  

Since your daughter is only 5, I would recommend waiting a few more years.  Kawai K500 is sufficient for now.  An upright piano with a larger soundboard (50 ~ 52 in) is as good as a baby grand.  When she becomes 9 or 10 and works on more advanced pieces, then consider investing in a grand piano that is at least 6'.  A bigger piano lets you produce more variety of colors and richer sound, not to mention helps you develop better technique, too. 

Of course, I would recommend a Steinway grand piano.  It doesn't have to be brand new.  But it's trickier to shop for a used or rebuilt Steinway piano. If you are planning to keep the first grand piano for 10 years or so, Yamaha, Kawai or Boston is ok but only a brand new one.  Be sure to get one with a bigger soundboard, 6' or more.  Also, this is very important part of owning a piano. Find a GREAT PIANO TECHNICIAN.  A great technician can elevate your piano.

All piano companies have sales. Yamaha seems to allow its dealers to offer more flexible prices. One of my students got a huge discount on her Shigeru-Kawai because it had a couple of small scratches on the lid.

My students are making great progress.  However, for students who have Kawai GX and Yamaha CX, I prefer recording them on my piano when we make videos. 

as a competitive pianist at 13 years old, my dream piano is a steinway LOL but my piano growing up was and has been a yamaha baby grand (from costco. literally.) 

you want to see how much she progresses further. wait until 12 or 13. if you want to really invest in her playing, i recommend buying a grand piano that has a better sound- like a yamaha. While kawai is good, it might not be as pleasing to listen to select pianists / something like that, seeing as it's japanese?? it has a different tone but if you grow up playing it it's beautiful (or so i've been told).

steinway is if you're rich lol! but anyways, i do recommend making her practice on the upright piano every now and then after you buy a grand piano, because of its differing tone makes her get more used to other types of pianos! in addition, you should add weights to the piano so that she has more power in her sound and a better tone!