The 6CTA8.3 aftercooler can easily be put on it's own cooling loop, there is only a single inlet and outlet pipe on it. Use an electric pump and some type of radiator for it like a trans cooler or such. This gets it off your engine cooling circuit altogether so you could easily and effectively lower its coolant temp by 100 degrees or more. This is good to 300hp level.
If you think you are going over 300hp, then this aftercooler is providing restriction to airflow, which is going to play a much larger part than reducing it's cooling liquid temp by 20-40F. The only way to correctly do what you want is to add the charge air cooler, and change the intake to a non-aftercooler type. That is what I am doing. Add said CAC (Charge Air Cooler) in front of radiator, then remove and discard this:
and install this:
Or, make the changes you desire and report the results so we can all value from them, but please report back with data so we all can learn (like 1/4 mile improvement times of 1 second, or blew holes in pistons #3, #4, and #6, with pics).
The HX40 may be an exhaust restriction also at that performance level, and that will drive EGT's to be high also. Make sure you are using the correctly sized turbo for your desired operating range (read and understand compressor flow efficiency maps). If you are still EGT hot at that point, then you can add a water/methanol (washer fluid) injection system.
There are a multitude of steps that can be taken, but total system comprehension is the best way of going about it. Learn how each part contributes, and its effect on others, within the entire system, to achieve the end result you want.
Source: Full credit to 4xdesign for his work and pics on the aftercooler and charge air cooler. When I spoke on the phone with him, he agreed a better path is to simply obtain the non-aftercooled intake rather than milling out the contents of the aftercooler.