If it's constantly slowing down and accelerating with load, it can't be too good i guess.. besides there's no benefit in making it constantly go from lowest speed to full speed. It will pull the maximum current many times per hour, or per day, instead of only once.

It's better to find a speed that allows your waterblocks to work properly, and stick to it. there's no need to vary the speed technically. It doesn't help with cooling and only stresses the pump electronics.

What's on your loop actually? radiators, waterblocks.. just to have an idea

well there may be a spot in between 30 and 100% that will get you going


an easy test to do would be to put your pump at full speed, and start some stress test, then reduce the speed little by little. The temperature of your GPU or CPU should go up just a little, but there will be a point where the temp will suddenly shoot up if you reduce too much. Just above that speed will be your lowest possible pump speed under load.
Then just add a bit of flow/pump speed to get some safety margin and you should have a fully working loop with very minimal pump noise, without even needing to vary the flow with load.

Depending on your waterblocks, a typical flow to cover all kinds of loads could be in the 80-120 l/h range.
you'll also see by looking at the temperatures that between that middle ground speed and full speed, there's almost no temperature difference. So it's not exactly worth it to run a pump at full speed.

The information about the required flow rate is all myths, you can find anything between 40 l/h and well over 100 l/h on the internet.
The temperature differences are in the range of a few K.
So if you want to see the lowest possible temperature you need about 150 l/h, I think that was the limit from which it makes no difference, if you want a quiet system you pick out the pump speed that sounds best to you, whether that is 40 l / h or 100 l / h, your system does not care.

the required flow depends on the waterblock design. some very bad ones like Corsair's need a ton of flow to get less-than-crappy results. Others won't care much until very low flows.
But again, when the temp shoots up because of low flow, it's like it will be ~10°C hotter than normal. in the absolute it's still completely useable no matter what flow.

On my rig, anything past 100L/h makes almost no difference.
70L/h is almost as good
60L/h gives me 8°C more on both waterblocks.

those thresholds are completely variable from rig to rig.