Members with 4 wheel disc systems: Can you lock your wheels?

Lack of stopping power can be caused by too many reasons, pad quality, to small of pads to rotor surface. I don't believe you have that problem due to the disc kits you installed, you've tried other size m/cylinders, I would look into more assist to increase the pressure with the larger bore m/cyl. When you went to the hydro booster what kind of pressure pump was recommended or was it a kit and may have needed different pulley sizes to increase or decrease pressure? I'm just throwing ideas out there for you to look into. I've read some of your builds you do great work.