Kitfox has extensively tested several brands and locations and they report near zero performance increase. Some have said they improve performance, but I believe that is their wounded pride and checkbook talking. The nature of the relationship between the flapperons and wing negate any benefit of...
http://www.avidfoxflyers.com/index.php?/topic/709-classic-iv-restoration/ My Kitfox build. I am not the original builder but have built more of this plane than he ever did. I still need to have an A&P do an annual condition inspection because I chose to keep the original airworthyness certificate.
By far the best performing engine is the Rotax 912 series of engines. They are light, powerful and extremely reliable. As to the propeller, this gets more complicated. The most popular is the Warp Drive 3-blade prop. They perform well, are very durable and affordable. Money and light sport rules...
http://www.avweb.com/avwebflash/news/13-Million-Judgment-Against-Mechanic-For-Crash-223632-1.html
I'd be willing to bet that every A&P and IA will soon be paying more for their errors and omission type...
http://www.avweb.com/avwebflash/news/Baseball-Cap-a-Factor-in-Mid-Air222786-1.html
Here comes the government to help again. The baseball cap was the reason for the mid-air collision.