Finatic,
I have a 1990 Gulfstream with a pair of 2004 F150's (with a flowscan meter) and they are pretty sweet setup on this hull. I average about 2.3 miles per gallon. I spinning counter rotating 17P stainless props. At 3400 rpms, I run 24-25 mph burning about 5 gallons per hour per engine or about 10 gallons per hour total.
At 4000 rpms, I am running 30 mph and burning 7 gallons per hour each engine or 14 gallons per hour combined. 4500 rpms sees about 35 mph and wot just touches 40 mph..I dont recall off hand what the WOT is, but it is right in the Yamaha recommended range.
I just went out and looked at the boat (she is still in the driveway) and they are bolted at the top bolt hole, but I had the tranny replaced last spring and they remounted the engines. I looked at the back of the boat and the anticavitation plates are level with the bottom of the hull....