Don,
I raised my motor 2 holes from where you mounted it. Cav plate is now 3.25" above keel. It still handles fine; can put helm hard over at most any speed with no ventilation.
I had a Doelfin on the old 115 and it seemed to help planning when I was heavily loaded on my Bahama trips; I could trim motor down and plane easily at 12-13 mph, allowing me to run comfortably SITTING DOWN in 3-4' head seas. When I added the 30" setback bracket and increased motor weight from 300 to 429 lbs, it wouldn't plane below about 18-20 mph! I added the Doelfin and that reduced min planing speed a couple mph, but it still wasn't as good as what I had before. I then tried a 4 blade prop and that got me back to where I was with the old motor. Denny