I have a similar issue in my 32GTR:
breaks down severly, only on full throttle, and only after about 4 to 4.5k rpm.
its got a Bee-R chipped ecu, looking to run about 1 bar.
I've tried changing plugs, tried a completely stock ecu, running back through standard boost solenoid.
compression tests at 160 across the board, with 150 on number 6.
But your problem is sounding very similar to mine, except i haven't checked my igniter yet.