Blow off valves should NEVER be in a twin set. PERIOD. They just make the problems worse. They open the compressors to the atmosphere and allow them to immediately over speed. Think about it, your compressor is RESTRICTED and is creating 90psi, then a valve opens that can dump it to 50psi...but the turbine side still has the drive pressure to create 90PSI. The energy has to go somewhere, so the compressor speed goes through the roof.
Boost is a terrible way to "support" power. You don't want boost, you want AIRFLOW. Boost, again, is a RESTRICTION. It's a necessary restriction in a diesel as you want boost, but you don't need crazy boost numbers to support "X" horsepower.
Properly designed systems (The complete package...head, cam, turbo, fuel) don't need gates.
Gates are nice. They let you get around certain issues like lag by running a smaller housing, then bypassing enough gas to not over speed the compressors and heat the air. Again, are they mandatory, no, but do they have their purpose, absolutely.
You don't need boost. You need air. There are plenty of people making stupid power numbers off of sub 60psi boost numbers. Personally, my best was 630ish horsepower at 38PSI. No wastegate, but it was a VGT. Headwork and cam, on a 98 12v.
The lower your drive pressure/boost ratio, the lower your pumping losses. If you can clean the smoke up at 38psi with a wastegate, pushing the wastegate closed and driving the charger to 60psi does nothing.
IMHO,
Chris