Hello,
We plan to insulate above our roof deck in Hawaii (2:12 pitch over most of the home, low/flat over a 20×15′ section) with Polyiso.
We then planned for a torchdown layer + white reflective coating (silicone – GACO, or acrylic – Western Colloid 720ARC).

However, I recently came across this product — FIRESTONE ULTRAWHITE
https://www.firestonebpco.com/us-en/roofing/asphalt-roofing-systems/ultrawhite-granulated-cap-sheet#

Comparing SRI (new/aged), it looks pretty good. Gaco is much higher initially, but does loose this over time (assumes no cleaning):
Ultrawhite Cap Sheet             SRI: 89/77
GACO S-20                               SRI: 111/76
Western Colloid 720 ARC     SRI: 84/75

QUESTION: What are thoughts on using a product like the Firestone Ultrawhite vs coating over this layer (torchdown)?

Thanks for any thoughts and advice as always!
Andrew