I can't give anything but my situation, but my prostate was 110gms weight at surgery, and 76cm wide by ultrasound at biopsy. The surgeon said it was the largest he had removed and it was the size of a small orange. He did a planned open RP, but had to do some extra cutting to remove it. He said if I had been having a DiVinci, I would probably have had to been converted to open by the surgeon, as the gland would have been too large to get out of the normal robotic surgery incisions. I don't know how large is too large, but with robotic surgery they excise the gland and attachments inside the cavity, place it all in a plastic bag and remove it thru an incision, so there is a point when large it too large.
Again welcome to the club now one wants to join and where no member wants to see an addition to the membership roll.