If a Holley tech actually told you 9 pounds of fuel pressure is ok, that only reinforces exactly what I’ve been saying about those jack off’s for years.
I would no sooner call them for teach advice than I would call...I’ll leave it right here for you to fill in the blanks. Screw Holley.
7 pounds is MAX and 6 is better. I use bottom feed needles and seats so I can run 4-4.5 pounds of fuel pressure.
Less fuel pressure equals more pump flow (as pressure rises flow goes down) and less pressure means less bubbles in the fuel. And yes, it matters.