Hello there,
I just came across this VERY interesting thread on my main lurking forum -
http://www.supraforums.com/forum/showthread.php?t=404955
In summary: If you run a 8awg cable (any thicker is no good) to a relay and use that to power the fuel pump, it will give you a bit more leeway on the stock Denso fuel pump as it will provide it with a MUCH higher voltage than the stock "thin" wiring is capable of providing, in essence increasing flow. Therefore, not needing to upgrade to a Walbro in tank pump.
Think this may help the people who are running their fuel system to the max by going BPU++ (Yoshi, Dave Prolex, etc). I remember Yoshi pointing out in a previous thread if he went to 19psi or even spiked to 19psi then his A/F Ratio went lean enough to grenade his engine.