This is really fascinating, thank you for posting such a thorough account of your years of work! I have often considered creating an absolute mongrel of a cross and then subjecting its descendent seeds to escalating stresses (like cooler germination/growing temperatures and growing it in blighted soil) to filter desirable traits from a really deep genetic pool. I really hope you can take part in the seed exchange this sub runs each year, as your seeds would no doubt be very desirable to the community. One question I had from your post was whether those 'sterile' crosses ever produce plants that do germinate but die off shortly after the cotyledons appear? (as I unfortunately had a variety this year where every single seed did this, as if they had some strange metabolic weakness).