Clean Drags? Or Clean Thermal Spread I reckon.
The difference will be small. I suggest you go dirty and reduce your heat elsewhere in the build. Clean drives might reduce heat a couple of percentage points and then only when maneuvering or accelerating or slowing down. When cruising or resting it's the same. Chain boosting though shows the dirty heat.
On top of that, clean drives draw more power than dirty, essentially cutting in to the thermal load you are saving.
The best way to make your ship run cooler is to reduce it's power draw. Clean drives just are not worth it in my view, and believe me I know as a former clean disciple that loves cool ships and has re-done all his ships with dirty drives.