I've driven a car with an ARC intercooler and a car with a larger intercooler that was apparently off one of the old NME cars. Both were very torquey and strong (bothat about 1 bar) and both owners said they'd got a noticeable increase in torque and response after fitting them.
I've also read elsewhere that a decent high-flow top-mount will give a similar increase ion torque to a decent front-mount, the only down-side is they still suffer from heatsoak.
No idea about running higher boost though.