I look forward to your results. It would be interesting to see how it compares to the Brilliant White from Carada as I think the gains would be close and the color balance of the BW may be better than the CW from what I've read.
When I heard that the JKP material was .9 gain and some of the arguments for it I wondered if was just a flat material like a matte white as far as where it sent the light, except with the .9 gain layer. I didn't think that sounded very special. But when I saw it I could see a slight hotspotting when I sat to the right more like the Studiotek 130 and although this might seem weird to some, I considered that a positive. That is, that it brought something to the table other than just being 10% dimmer than a matte white screen. I haven't measured the different angles, but a screen with the directionality of the Studiotek 130 but a .7 gain layer for a .9 gain rating instead of 1.3 and combines that with looking fairly smooth compared to the Grayhawk RS brings something to the table. Any screen with directionality can be downgraded compared to a matte white screen in any review just for the directionality, but that directionality is bringing something positive to the table for certain setups. It is basically ANSI CR retention in real rooms and added ability to reject off-axis lighting compared to what happens with the projected light (which gets a higher average gain when things are setup right).
I should say that since I haven't done measurements my eyes may have been fooling me (or the projector in use could have had some non-uniformity causing what I saw) and somebody will report that it is basically just a matte white screen with 10% less gain everywhere, but from looking at it I thought it had a slight gain that would make the center of the screen a little bit brighter than the corners for a center viewer relative to what a matte white screen does. Given that CRTs tended to have falloff toward the edges and digitals don't to the same degree, a screen with some falloff for a center viewer can take things to more like what CRTs tended to give. While that can be a negative, it could also help the darkest scenes appear darker as the difference between the edges of the image and the screen frame can be lower.
Screens are complicated and I think people need to take into account that when starting from a matte white base certain changes will make the screen better for certain setups, but worse for others. For instance, while I realize it was a simplification, I don't really agree with some that a perfect screen will send light uniformly everywhere. If nobody is sitting at far angles then the perfect screen IMO wouldn't send a bunch of light over there to hit the wall, come back to the screen and degrade the images for the actual viewers. To my eyes the JKP .9 gain screen looks like a reasonable screen for rooms with some reflections to fight and with a bright enough projector that .9 gain is reasonable.