They do sell the stock Bosch pump. But they also sell their "high volume" pump, which looks like the Bosch pump with their own turbine housing on it. It is supposed to pump an extra gallon a minute.
I've been watching this conversation and have some input that may help. First question, does your intercooler have air trapped in it? Without liquid in full contact with all the internal passages it will be far less efficient at pulling the heat from the intake air. The DF intercooler, at about 110 cu.in., should be big enough for 300HP, as long as the air is fully purged and the heat exchanger is working properly.
Next is the fluid pump. The Bosch pump is rated at 5GPM with zero pressure or 2.5GPM at nominal operating pressure and even less if there are coolant line restrictions. 2.5GPM should be adequate flow for the stock DF supplied intercooler and heat exchanger (based on the approximately 90 sq.in. front surface area of the core) as long as enough 'cold' air flows through the exchanger.
Air flow is key through the heat exchanger and is hampered by the stock mounting location, being exposed behind the radiator in the expelled hot air and lacking any 'directed' air flow as mounted. The air behind the radiator, with the open bottom and sides in the bodywork, is highly chaotic and it's possible a hot air eddy could form above the heat exchanger. The NACA ducts may help, but only if the air pressure coming into the ducts is higher than the air pressure under the heat exchanger - no air flow if the car isn't moving. Using the fan only will either pull air from under the car (ideal) or push already heated air from the radiator through the exchanger, depending upon how the fan is connected. This brings up the second question, is the fan pulling through the heat exchanger from the bottom of the car?
Using the fan - set up to push air through the heat exchanger from above - plus the NACA ducts into the heat exchanger with the stock parts is the best solution. No radiator hot air and the exchanger will see constant air flow. There are a few builders who have used this combination and may be able to provide more info how to set this up.
Some discussion has already touched on using a larger intercooler and having one with larger internal volume, in cubic inches, does two things for you. It slows the airflow down to exchange more heat into the internal fins and provides more thermal mass that takes longer to heat up. On the downside, it takes longer to cool down if the heat exchanger is not efficient enough or is undersized. A good way to know this to compare the cubic inch volume of your intercooler to the cubic volume of the heat exchanger. The closer to a one-to-one or bigger on the heat exchanger is adequate sizing.
Alternatively, a secondary heat exchanger, in addition to the stock DF exchanger, would be an ideal way to see if the intercooler is adequately sized for your turbo and HP. If by adding more heat exchanger volume the IATs go down you've solved your problem. If the temps don't reduce, it's likely a different intercooler may be needed - and you already have the heat exchanger cooling required for a larger intercooler.
This is my 2 cents on this problem.