Reporting back after my first ride with the ZRACE XG calipers hooked up to LTWOO RX. Did a bunch of hill intervals, about 200ft/60m elevation on each, with decently steep terrain--so you could say it's a fair test.
Nothing too interesting re: power and modulation. It's about the same as the OEM LTWOO RX brakes. Brakes generate a TON of dust though, compared to the RX. My only point of reference are Shimano XT and Sram Rival hydro brakes (the original iteration)--I would say this setup definitely has better power and modulation compared to those old Sram brakes, and approaches that of the XT brakes.
Didn't detect any brake fade. That being said, I've never experienced brake fade, I think you really need to descend a serious mountain to experience that.
These brakes are light and look sharp, but I have to say, I am disappointed by how wide they are. They are a full 5mm wider than the LTWOO RX. If you care about marginal gains, these are definitely less aero than the LTWOO calipers, and I think that's nothing to scoff at. Most brakes will hide nicely behind the fork legs, but on the XG calipers, the cylinder port stands proud of the fork's silhouette. Having an extra 5x10mm square section in the wind near the leading edges probably costs a watt or so.
Now, the weight is really the big win here. Sub 100g calipers with pads is a big deal. Haven't done a final weigh-in on the bike to see what the improvement is, but I will report back once I do.