I don't know if the improvement with a 40 is going to be worth the expence. When the trim bar is set just right, I don't think you'll improve more then 5mph top end at the most. Have you thought about selling the 40 and looking for a good used 50-60 with factory tilt/trim? That way you can get a good hole shot and really feel the wind in your face.
I just put a used one on my 17' Bass Tracker Mod-V Hull Jon boat W/ 40 HP Merc. I love it. It allows for EASY raising and lowering for running slow in shallow water as well as easy raising for loading on the trailer....New they are expensive. I found mine on Craigslist for $300.00 and only had to drive about 10 miles...works great....and it did increase top speed a little....sort of like a "Jack Plate" with power trim and tilt...