I just completed an electric conversion of my butterfly. I ended up using a nippy black 2510/14 ($56.90) brushless motor from Hobby-Lobby.com, CC25 amp esc and 2 1500 mAh 7.4V LiPo batteries wired in parallel to get 3000 mAh. I am also using a 11X4.7 APC prop. This setup pulls 15 amps.
The only problem with this setup so far is that I had to add a lot of weight to the nose to get the plane to balance. My total weight ended up being 70 oz. Lucky for me the motor is good for sailplanes up to 70 oz. I flew the plane this morning and it flew just fine with the extra weight. My plane is a slow lumbering giant. It has a slow climb rate and glides real well. This is the mission of my plane and I feel I have achieved that. The only change that I am going to make is to replace the LiPo batteries with an 8 cell 2600 mAh Nicad battery that weights just as much as my current set up.
Before I did the brushless setup I used a brushed motor on a gearbox with a 7cell battery. This setup worked just fine for one flight. My ESC had a break and it damaged the gearbox. If you would like some more info about my brushed setup I will give what info I have.
Good Luck