What engine? What torque converter do you have? If you have a stock converter, a swap to a good converter could be worth several tenths. Way bigger improvement than the gear swap you are considering. The 904 low gear set seems to be worth about a tenth on this site. The 3.23 to 3.55 swap might be worth a couple tenths. Just speculating here. Very application specific of course. IMO, the closer the converter is to being optimum for your combo, the less difference a small gear change will make.