When I make any changes like that, I try to make back-to-back comparisons at the track and let the ET/MPH tell the story. But you have to make sure that "YOU" do everything the same to make sure the jets are the only variable.

Any changes may depend on where you were to optimum jetting to begin with.

Just my theory, but I figure that the added plenum volume, especially due to an open spacer, can reduce the vacuum signal. That may require more jetting and possibly added accellerator pump volume and/or duration.