Ben, you need to stop thinking about boost as power. Closing the vanes will give you more boost but drive pressure will rise exponentially when you get out of the turbo's effeciency range. Opening the vanes will lower drive pressure and bring the turbo back into it's effeciency range, it will also lower boost, but it will gain power.
Adding a wastegate would be to bleed off drive pressure when opening the vanes completely isn't enough, which if anything would also lower boost. We have an LLY with a stock charger that has done over 600 rwhp on 2 different dyno's including Dave Dunbar's - he is still in the mid to low 30s for boost. After swapping in a BatMoWheel he gained 32 peak hp (up to 636 rwhp) and put more power under the entire curve, all while running slightly less boost than what he did on the stock charger.
Power isn't about how much boost you have built up in the intercooler, it's about how much air you are moving through the motor. As drive pressure goes up the motor will be able to move less air, as the motor takes in less air more gets backed up between the turbo and motor (boost) but less power is produced.
