Most people with dual Walbros run the second one either on a Hobbs or progressively (BlaqOPs) and not always-on. My Bosch 044 would over-run the stock fuel pressure regulator at idle (52psi). The stock return line has no issue with an aftermarket afpr installed.

Many people use boost-a-pumps to run their pumps at 17volts (on a Hobbs). I haven't heard about any meaningful reduction in pump longevity as a result. My single 044 can put out as much fuel as dual 255's on the BAP. Yeah, it's louder than heck but that isn't a consideration with my car.

 

I used to firmly believe that the return lines were to small, but now I am not so sure. I use an AEM fpr with the medium sized return port installed. I have a Bosch 44 under my LH rear floor that is fed by a walbro in the trunk. Since Tephra posted up the minimum injector pulse width patch for cars running 1500cc and larger injectors, my car will stabilize its idle just over 15.2. So perhaps the stock return lines are fine, at least on my set up.

Pump noise... I can't hear my Walbro in the trunk at all. Even with the trunk open and my head in it. It is mounted in a foam sleave though that soaks up nearly all of the vibration. The Bosch...... well, loud is a matter of perspective. I am somewhat hard of hearing from working on jet aircraft for so long.

I really think the most reliable way to eliminate the relay issue is to remove the relay completely and install a jumper wire (12awg or larger) or to do that and install an after market relay. When the after market relay fails, your car won't run. Very few cars have engine failures while not running......

 

From my experience the return line has to be able to handle the flow of a pump or dual pumps at full voltage and not cause a dramatic increase in pressure. The restriction of the return line is the tank. But you are considering running some like AN 8-10 the ~AN 4 return that is stock will be barely sufficient to handle the flow from larger pumps.

The return has to be either a equal size to the fuel feed or one size smaller is typically fine.

 

I'm not sure if this applies to the X, but I figure I'd bring it up just in case: We shant forget about the TedB mod to the syphon venturi that properly reduces fuel pressure at idle.