Understand the needle restriction, free flow was just a term and I'm sure you understand what I was talking about without further explanation. As before, need a test to verify either of our assumptions

I'm not assuming. I assumed as you many years ago, and then the years and experiences went on.

Have ran into it on the water, at the track, and the dyno. Under 4lbs was an issue. Typically engine would go flat,no more rpm, and be lazy at that final rpm. 3psi and under, hold your nutz. lol

Once on the dyno I stood next to the engine as it had glass sight bowls. AF would shoot up, engine started to break up, and the fuel would in the sight glass would turn into a brothy mess.

Not assuming here either. It's basic physics. It takes X amount of press to force a fluid thru a restriction to achieve an X amount of flow.
I've personally seen the effects of low fuel press at WOT many times and it's never pretty.

Sounds like the OP is on the right path. If there is significant wear causing the fuel pump to not move thru it's full range of motion, that could cause low fuel press at WOT. Especially with an over-driven blower on a BB.

He ended up borrowing a used Merc pump, threw it on last night and saw 7.5lbs at idle and 5+lbs at WOT, good to go, I guess something was wrong with the brand new sierra 18-8860 or it wasn't the correct pump to begin with

I also did find on Holley website that they state the 1050 Dominator should not go below 5psi, i see what you guys are saying about low pressure high flow, but 5psi min pressure must be needed to maintain a safe carburetor operation