Generally it's good to keep it under 40C, obviously a bit more leeway for SFF builds on limited rad area. The conservative target you usually hear is keeping coolant no higher than 15C above ambient temp. But the water temp is way too high for the size of your loop. In a max all-out CPU stress like AIDA FPU or LinpackXtreme, 70-75C is pretty reasonable for 5900X under water (under air LinX can regularly hit 85C+ on mine). The 5800X build has an ASUS KO GeForce RTX 3060 Ti OC 8GB graphics card with the stock cooler it is generating less heat than the 3080 Ti in the 5900X build. The motherboard temps max out at 45 ☌ in both builds so the cases are adequately cooled (motherboard idle temps: 33 ☌ for the 5900X build, 35 ☌ for the 5800X build). That's partly why I haven't bothered to swap out the EVGA AIO with the CoolerMaster one. Both systems have lower CPU max temperatures during gaming. The only times they really reach those maximums in prolonged real world usage is during Handbrake encodes. When I had the 5800X paired with a CoolerMaster MasterLiquid 240 mm AIO it ran much cooler. The 5800X reaches a much higher temperature because the EVGA AIO has a pretty small Asetek cooling block. Like my 5900X build, the CPU AIO fan curves are set to max out at 1000 rpm. That AIO is nothing special and the CPU reaches close to 80 ☌ during a Cinebench R23 run but the AIO reports a liquid temperature of 33 ☌. I also have a 5800X in another build cooled by a vanilla EVGA CLC 240 mm AIO. The CPU radiator fan curves are set to max out at 65% (about 950 rpm). My CPU waterblock exhausts to the thinner 360 mm radiator since the 5900X generates less heat.
Note that my inline coolant thermal sensor measures the exhaust of the GPU waterblock before it enters the thicker 360 mm radiator. My 5900X build (the one described in my system specs) maxes out at 52 ☌ CPU temp (during a Cinemark R23 run) and 43 ☌ thermal sensor temp.