The adjustable proportioning valve from Wilwood is an excellent piece; it is adjustable because every combination is different, and this can require subtle changes in proportioning to give the best braking performance. If you plan on ever throwing your ride through cones, the adjustable valve is a good choice. Although the factory-style combination valve is ok with a stock disc/drum setup, it is a compromise, with no adjustability. It includes a metering valve, which will delay the application of the front brakes momentarily, in order for the rear brakes to overcome the return springs, and help control brake dive. Although it is a nice feature, it isn't critical in a properly balanced system. Controlling rear brake lockup is always critical, and a good proportioning valve is the best way to do this. Adjustability just lets you get it "perfect" without disassembling the system.