Thank you Wishgranter,
I will try to process the 2500 img data chunk with those settings and report back.
Won’t having a lower feature reprojection error lead to a better mesh?
The overlap is of 90% so using the central area of the image shouldn’t be an issue right?
Its great to understand preselector now 
I guess that it will take the 40k best points out of 80k?
Kindest regards,
Manuel Franquelo.