If I do a hard 1-2-3 pull at 10 PSI, I see about a 10 degree C rise in temp above ambient, and it takes about 15 seconds to get back to near-ambient. The sharpness of the rise begins to drop off at about 100kph as the intercooler begins to get significant high pressure air.
I heard from Bear you're getting some crazy MATs, but I would expect that for a few reasons on your setup. If you're running a different pulley for more boost, you may be exceeding the efficiency range of the compressor, and the small air-to-water cooler may not be as efficient as you need it to be.
You might want to look into a cheap, larger cooler from fleabay. Since you already have all the plumbing, etc, you might just need some modified intake tubing and you're off.