as you normally measure boost pressure in the inlet plenum, the pressure drop across the pipework and intercooler is largely irrelevant (except of course that a big pressure drop would mean overworking the compressor and making it very inefficient adding loads of heat)

having bigger diameter pipes will not really achieve anything - the majority of the total pressure drop between compressor outlet and TB will be the intercooler.

it's all very well saying that in theory big pipes are better, but you have to keep it all in relation to the biggest restricition which should always be your target for improvement. having 5" boost pipes either side of a intercooler with tiny tubes would achieve precidely zero. it would be like having a 5" downpipe and exhaust, and a standard backbox