RustyNuts,
Firstly, welcome to the forum...
There's people on this forum making 500 HP normally aspirated and 1000+ HP boosted (and they have done this using EFILive on the factory PCM).
A good tuner with a wideband and a dyno can certainly extract every bit of power and torque from your combination;
and, a DIY tuner with a wideband will be able to do almost as good (and as good in many cases).
The factory PCM is
very capable, and provides features such as engine protection mode, misfire detection, diagnostics, and automatic transmission control (shifting, shift firmness, shift points)... and you don't need to rewire your vehicle.
EFILive supports wideband inputs and has conversion pids for most available widebands.
As Maggie said, EFILive provides several custom OS's which support boost and nitrous (among other features, they provide extra tables for fueling and timing).
Also, Craig Moates makes the "RoadRunner" (which is a real time tunable version of the factory PCM) with which EFILive software can make on-the-fly adjustments (e.g. getting VE table tuned from wideband data in real time as you drive).
Cheers,
Joe