Cricket Tragic, This paper talks about some of the aspects of gene flow from GM to wild and tame relatives.
http://washburnlaw.edu/wlj/43-3/articles/glenn-jane.pdf
"Organic farmers have the most to lose, as they risk not only their markets but also their certified organic status if their crops become contaminated with GM genes. The level of contamination of canola on the Canadian prairies is such that this crop is now lost to them,
and they are concerned that other crops, notably wheat, may equally be lost."
One of the points being that the biotech companies are demanding the right to compensation for all future seed arising from their patents, but steadfastly refuse to accept responsibility for the economic harm caused by the same seed.
I note that the references you posted in particular the PG economics papers suggest that organic growers in Spain could solve a lot of their own problems if they would only have the good sense to loosen their quality control regulations with respect to allowing GM into their product. An interesting argument given the losses incurred by north American farmers who haven't had the benefit of the barriers required of GM producers in Europe.