I run a 38mm gate, mounted between the crossover and down pipe where they pass beside each other right underneath the driver side floor pan/firewall. So far, I've had good luck with this method with boost control and longevity, so we'll see how it works out on the 5.0L. I have been able to go as low as 2 psi, and as high as 16 psi on previous builds, granted they were Turbo Chevy LS small block setups.
Can the new PCM speak boost? Can you map a boost controller output using the PCM? It certainly is good to be able to control it electronically, and from the PCM itself (throttle position, RPM) rather than a simple max boost wastegate pneumatic control.
The setup I used years a go was a solenoid cycling between manifold pressure and atmosphere using a PWM output from the PCM (aftermarket Autronics unit) with the resulting controlled pressure applied against the wastegate diaphragm. Electronic control pneumatically actuated.