Im using low fin rads too and i find i need a lot of them to get a decent amount of heat removal if i wanna keep the fans running slow, im actually using 2x240s a 360 and a 480 and if i just leave my fans at 800rpm my loop will eventually get too warm. I would suggest switching your fan speed control to you GPU temps as theyre much closer to the loop temp and more stable than the CPU, this will stop them speeding up for now reason when you CPU is under load for short amounts of time.
Install speedfan theres loads of guides to help ya set it up on youtube, and set up a fancurve for your GPUs, i would set it up to keep your GPUs below 50, this will keep your loop around 40 and stop your CPU overheating.
Install speedfan theres loads of guides to help ya set it up on youtube, and set up a fancurve for your GPUs, i would set it up to keep your GPUs below 50, this will keep your loop around 40 and stop your CPU overheating.