Fuel pressure

How much fuel pressure will a Holley handle? I have had a problem trying to get a handle on my Sixpack jetting. Lean just driving around, stand on it and black plugs.
That's with stock metering plates in the end carbs. Finally got an inline fuel pressure gauge and I have 10 lbs. I am using the Carter M 6270 pump. It's the only pump that with stock type ports for a say '69 or '70. So I need to regulate down to 5 or 6 right?