There is nothing wrong with using a bleed valve, it's a valuable tuning tool, and provides easy adjustability of boost without the risk of wastegate creep.

It is true that not using the amal valve removes the boost cut. Howver, this kicks in rarely, eg Limp Home mode, very hight temps etc. Providing u keep an eye on ur gauges etc, u'll feel the car the car not driving right before any serious damage is done. Limiting the boost wont always help the problem anyway.

To run 20psi, u simply have to have the available fuel, and have the rest of the engine components able to take the increased compression pressure and heat. With beige injectors, ur not going to have the fuel for much more than 20, especially if the engine is modded with cams and heads etc.