Just found a few comments while searching the web.
"In designing intercoolers, most vehicle manufacturers design them for the optimum workings of the engine, and the vehicles working conditions. In general the misconception is that fitting a larger intercooler will work, this is not the case as the manufacturers have already provided the optimum for the vehicle. This is also matched to the fuel injection system, as this will also provide the optimum fuel for the cooled air, so fitting a larger unit will often create more fuelling problems.
Fitting two units will not be viable as this will create more internal air friction, thus depriving the free flow of air to the engine. If this were a better option it would have already been done as an inter and after cooler.
Intercoolers are matched to air flow, and air requirements, and as all diesel engines receive a surplus of air anyway, whats the point of supplying the engine with an even greater surplus of air.
All in all the claims made have been disproven by me and many others, time and time again; unless there are other modifications to provide substantially more fuel to the engine, then uprating the intercooler is an expensive waste of time."
"Stick with the stock intercooler if you are using the stock turbo. Yeah, some people claim some gains with upgarding the intercooler but perhaps there are other loses as well(spool up and lost of boost)."