Depends on a lot of things. A 4 hole will usually give you a little more bottom end, but it's really build defendant. For instance when I built my 408 I used an Eddy air gap and I tried a 4 hole and an open spacer to look for improvement and it liked the open better. That's typical with a larger cubic inch engine as they can use more plenum volume than a smaller engine.
BTW: I assume you must be using non-ethanol fuel for 12.8 to be rich enough? I can't get anything (at the pump) that doesn't have ethanol in it so it like an afr of 12.2-12.3 the best
