So I tested a bit more this afternoon, and I saw a full throttle run where I dropped to 45 psi! That's no good...
I discovered that the Holley HP EFI will actually give me a Fuel Flow calculation as one of the pieces of data in the Datalog. If the number is to be believed, then it showed a max value of 299.2 lb/hr. If your 5th Gen pump number of 255 lb/hr is right, and my Holley number is right, then I'm out of fuel pump.
That would seemingly make sense, but it's also a bit surprising to me. I need to go back and reread the Vaporworx threads, but I thought the 5th Gen pump was the recommended setup. Maybe it's only good up to about 500HP or so?