http://www.saunalahti.fi/lunden/varroakertomus.htm, and it is quite interesting I suggest you do. One of the first things he suggests is "There will be more instrumental insemination in the coming years. This is because the risks are getting bigger: one wrong choice, one drone-line that is not working as expected, would be a big hit back. "
What I think he is eluding to, is once youve sort of hit the nail on the head with what you want for genetics, if you have a wild card drone in there it will inject those genetics into possibly your whole apiary. To that effect I think he is right. His breeding plan is actually quite a well thought out operation, but very intensive.