I'm sure things like flow rates play a bigger role than temp. How slow is the mash move through the heat exchanger vs the water/glycol flow rate. Below an expert says glycol is 10% less efficient but I think that is a blank statement lacking specifics.
Various expert comments found online - "water temperature capacity vs glycol"
"Water has a better ability to retain and conduct heat from an associated process than a glycol mixture can. As a result, the efficiency of heat transfer for a water chiller will be higher than that of a glycol chiller." Why we have our chiller setup without glycol.
"Water has superior heat transfer properties compared to propylene or ethylene glycol and is more frequently used in the southern half of the United States. Water is also cheaper than glycol and, in most cases, will result in a smaller unit selection while requiring less pumping HP."
"Water is the most common heat transfer fluid because of its economy, high heat capacity and favorable transport properties."
“If a system is utilizing glycol, instead of pure water, that mixture has a different heat transfer rate with potentially five to 10 percent less efficiency than water due to its viscosity,”