Try running with tabs all the way up, tap drives up, up, up, up, until the props start to blow out, or your speed drops off. (I'm assuming you are using GPS for speed?). But, no full tank, 1/4 or Two people max in the boat. No water/gray water tank stuff. No extra weight of any kind if possible. The test in 1999 of a stepped 43 with the 470HP 500efi's was 74 mph.
There should be no reason to use any tab at WOT unless you are loaded unevenly, cross wind to level, or the water is so rough you don't want to fly the boat.