Good question, so this is my impression so far.
Prior to the permatrim I felt the boat always rode with the bow in the air (more than I like) and would apply trim tabs to push the bow down and level out the ride. Doing this improved the ride, but my mpg seemed lower. No detailed analysis, partially because the swell was usually more at the same time i pushed the bow down.
Knowing that the Parker is known for this I borrowed a 4 blade prop as it is supposed to push the stern up. The prop I borrowed pushed the stern down and I got a better ride, but my mpg dropped and the motor always seemed to be working harder. The top end dropped a lot as well. I changed back to my SSII 17" and added the permatrim.
With the permatrim, the boat rides more like the 4 blade, but I have the stern lift and the boat seems to drive more level and even in the rougher conditions i've been out (2x so far) it has been noticeable smoothing of the ride, but my mpg remained solid. Both trips have been short distance (less than 30 miles each) and the short interval swell that makes it tough to get a solid high end run. I plan at about 18-20mph now, compared to 22-24 before. I've attached a few pics from my run back from Crystal Cove to Dana Point, about 10-12 miles.
For reference it was me (i'm 300+lbs), 120gal of fuel and 1/2 a bait tank (65 gal full) and all my crap and ice.