Hi Steve, thanks for a great review.
Looks nice. It is a shame though that a PJ at this price point is still going to need an external 3DLUT solution to have colours that track through the whole gamut accurately, especially when you consider that all the electronics you'd need for a 3DLUT is undoubtedly already in the box (save for a little bit of flash memory to store the 3DLUT, and perhaps a slightly larger FPGA).
The JVCs absolutely don't need an external 3D LUT as long as you use the excellent and free JVC Autocal software to get an almost perfect baseline, both for gamma/greyscale and gamut.
What Steve reports is the best you can get with the internal contrals, which are very limited as you have only 2 point greyscale, tri-band gamma and non-working CMS.
The JVC Autocal software, which requires a Spyder 4 (possibly Spyder 5 soon) sensor gives you up to 33 step gamma autocalibration, 12-point manual gamma adjustment and near perfect gamut calibration provided you create a custom rec-709 colour profile (and the specific Spyder 4/5 unit you use is reasonably accurate).
The calibration is done at 75%, perhaps I didn't make that clear. The point I was trying to make was that the tracking out-of-the box is excellent from 75% down, so you just need to tweak the CMS rather that dialling in perfect results which is what I did initially. If you over use the CMS it begins have an adverse effect at 25 and 50%. The X5000 can be calibrated well using its own controls, I only mentioned the Prisma because I happen to be reviewing it right now.
This is the way the JVC CMS has always worked sadly, on current and past models back to their first CMS on the HD-750. It was definitely there on my X7. That's when I first reported it and it's been there since, but as most people were not checking linearity, they just produced great looking charts and undersaturated calibrations.
The internal JVC CMS does generate undersaturated calibrations if you aim for 100% of rec-709. It has always done. The only way to mitigate this is to calibrate to 75% of rec-709, as you have done, but it's still not ideal. As I - and others - have reported this to JVC for years now, it's quite clear that either they don't understand the issue, or they can't solve it. The CMS is best not used for this reason as it messes with the gamut linearity or leads to an oversaturated calibration at 100% sat (there isn't much real content there, except maybe with animation, but still).
This used to lead to the need to get external calibration until they offered the JVC Autocal software. Now, with this software, you can get in most cases - bar an undersaturated / uncorrectable gamut to start with - a near perfect calibration.
Regarding how much of P3 the X5000 can cover, you might want to use the JVC autocal to create a DCI custom profile and see how much of P3 you measure with this.
Just like creating a custom rec-709 colour profile gives you much better results (fully correctable, excellent saturation tracking), creating a DCI colour profile with the JVC Autocal software would ensure that you are actually getting the widest possible gamut the PJ can offer.
Alternatively, you might want to try with colour profile off, not with the cinema profile you have used, which is wider but is likely not the widest possible gamut the PJ can offer.
I and others have documented the JVC Autocal software in the other forum, so you might want to take a look and see how it works. It has a steep learning curve given the lack of detailed documentation from JVC, but it's a well worth investment, and in my opinion the only way to get the best out of these projectors, especially without any external correction.