Sure, but i think the best way would be to run a chip. You'll get better boost response, better economy (not always) and most importantly the removal of your boost and speed cuts, no point in raising the boost if you hit the limiter.
What turbo are you running? you might have picked up a Psi or so with the exhaust and intake, are you running a highflowed dump pipe?
The best way to increase boost is with a chip, as the chip changes the Air and Fuel to match the increased boost.
You get what you pay for, I mean how much info can you get about the map on it?
Have they tested it on similar vehicles? whats the AFR under power, wastegate spring psi etc
16psi is the limit, but you could run an inline restriction to taper it off.
380s will be good for around 180kw at the wheels after that 440cc yellow tops from V3/4 STI and you'll crack 200kw@wheels.
Then you'll have to go aftermarket and require a Tunable ECU.
You've gone single on your GTB? try and fit the clam shell heat shield over your heat wrapped down pipe that would be best, rather that just heat wrapping it.
If you still have the twin setup then just leave it.
Car: 1991 series 2 RS type RA
Suspension: Tein superstreet coilovers
Mags: Speedline type 2013
wheels diamater: 17"
Wheels width: 7"
Offset: +48
Tyres spec: 215/45/17
did you have to roll the gaurds?: Rears only
Another point, have seen a few speedo cable on early RS and WRX eventually harden and seize the cable due to heat from the downpipe (not to mention my own)