5-6 psi is a huge difference over N/A.
on my old combo with thumper heads and b-cam. best i mangaged N/A was 13.3
103
added an SCtrim with a UPR boostmaster pipe, with 6 psi i manged 12.1@113.
made a big difference.
and NO you wont be happy with 5-6 psi, its a good difference but its so easy to swap pullies and make more boost. i added a crank pulley and made around 9 psi.
i picked up a few MPH to 115 but never got a faster E/T due to traction issues. i did managed the same 12.1 but with a slow 60'.
i ran the combo untuned, with stock injectors and an FMU and ended up blowing a HG.
over that winter i upgraded to some TFS TW heads and an f-cam. got it running again and this time i used a tweecer and 42lb injectors. and tuned the car properly. boost dropped to 7 psi with the head and cam change, but the car quite a bit faster. later on i threw a smaller blower pulley on and make 12-13 psi. the car ran REALLY good then.
never got back to the track but i would have guessed it would have been in the 11.5 range at 120ish MPH maybe quicker. it was a quite a huge difference with the better heads and cam and more boost.