usually after installing a cooler you will notice a small (realitivly insignificant) pressure drop. the turbo outlet pressure may be 10psi but gauges taken from the inlet plenum would be less, 9psi for example. some of the pressure is lost in getting the flow through the cooler and pipes to your engine.
fitting an exhaust will help it to spool up quicker, exhaust coming from you engine is under pressure and being released into the dump pipe through the turbine housing. the bigger exhaust creates a low pressure at this point so the exhaust gasses will speed up, hence your turbo spools up quicker and can maintain a slightly higher rpm. more turbine rpm gives more compressor rpm which gives more boost.
anyway enough rambling, did you know if its the standard wastegate actuator? one of a 32 can bolt on and will produce 10psi.