All I can say is from my own experience. My first cycle, the doc was very cautious and I had low stims, only produced about 10 eggs, 9 were mature and fertilised and of those 5 were normal. My next cycle my doc went a little heavier on the drugs but I way over stimmed and ended up with about 40 follicles, we still retrieved the same amt of eggs but they were not as good quality, I only ended up with 4 normal even though there were all those follies on the u/s.
Thankfully for me, I did get my son from that cycle, but it was just sheer luck. I do believe less is more.
If you look through all of the PGD stats on here, you will see that a lot of the time ladies who retrieve 20+ eggs still only end up with a similar amt of normals at the end compared with those who only retrieve around 10 eggs. In saying all of that, you don't want too few eggs either 'cause you need a few to work with, I hoped for around 12, not too many, but enough.