Going back to the question of why will a bigger intercooler mean less boost, im crap at thermofluid science but I might be able to add somthing.
Any system carrying a fluid will suffer a 'head loss'. This is due to the energy required to move the fluid being taken from its pressure. Flow rate must stay the same. So there will be a bressure differentia between the inlet and outlet of the IC. BUT, it will flow the same amount of air in as it does out, so I might be right in thinging that it will just create more pressure between the Glader and the IC, because the IC is acting as a sort of 'resistor'.
All a bit stabbing in the dark, I should have payed much more attention.
