My paper of choice, and my client's, for a non warm photo surface, was always Hahnemuhle Photo Rag Baryta. After using it extensively for an artist who consistently had large smooth areas of light color, and also large clear white margins, we could no longer deal with the flecks in the paper, despite generous help from Hahnemuhle for years. Finally we switched to Hahnemuhle Photo Rag Pearl, and can not see the difference. Hahnemuhle Photo Rag Baryta, being cotton, feels softer to handle, but visually the prints are nearly identical. I would still recommend Hahnemuhle Photo Rag Baryta for prints with a lot of detail, ink density, with no need for clear margins, it's beautiful paper. These papers measured close to neutral, I would not call them cool, except by comparison to the warmish papers, of which there are many excellent choices already mentioned in the thread. To get cooler I think you have to go to papers with OBAs. The only brightened photo surface paper I have seen a lot of with the Cone + GO system is Epson Exhibition Fiber, and the Innova equivalent. The WN set looks very much like untoned chlorobromide paper, a bit olive, and the selenium set looks nearly indistiguishable from a toned bromide print. The GO pass marries the ink to the surface in a unique way. I worked for months on a single pass version for convenience, but double pass was the answer. I think the HP performance bears that out.
Back to the topic, I think you're going to need a paper with OBAs if something like Photo Rag Pearl is still not cool enough for you. The Epson works well, Harman gloss still exhibited some chromatic reflections, as did Pictorico GEKKO Green.