MLESAC instead of RANSAC ?
Is MLESAC available for OpenCV C++?
It should be much better than RANSAC. Source: http://www.robots.ox.ac.uk/~vgg/publications/2000/Torr00/torr00.pdf
I have only found for Matlab: http://graphics.cs.msu.ru/ru/science/research/machinelearning/ransactoolbox