Ok, I know the directions say 1/16th in 6 feet or 3/16th in 10 feet, but in your real experiences, how flat is "flat enough" for the subfloor to install 3/4 solid hardwoods?

Frankly, I've spent months of time and money to jack up the main beam of the house and resupport with new lally columns, jack up and sister in individual floor joists, rent a edger to sand down high spots, and feathered out low spots with a combination of thin plywood, shingles, and felt paper. The floor is significantly better in terms of flatness, but there is still areas that are not flat within those specificiations listed in the instructions. I would say 80% of the floor is within those specs but in some areas I have variations of, at maximum, 3/16th in 6 feet or so and I can't get any better without creating other problems (i'm at the point if I flatten it one way it will not be flat if I put the straight edge perpendicular to it).

In real world expeirences, how much of the specs in the instructions are the manufactuer covering its butt, and how much is realistic? What will happen if I install it now? Out of curiosity, I checked the flatness of my parents house that is 10 years old and has some hardwoods, and my brother in laws who is 25 years old and he just put in hardwoods-they don't creak or anything and with a 8 foot straightedge these houses have settled and are not within those specs. Now I have an 80 year old house with much more settling, and just want to know what to expect cause, frankly, the sublfoor is not getting any flatter without tearing down the house and building a new one.

Realistically, on wood subfloors that are older, they are never in spec due to settling of foundations and sometimes, houses not built well to begin with. With UNFINISHED flooring that is to be sanded in place, high spots can be ground down a little more after the floor is in. With factory finished floors, you don't have that option. Now, you can install that floor, and probably 90% of people would never notice it isn't flat. I have laid solid, 3/4" floors over subfloors that were "out of spec", because the owners did not want to invest in repairing them. It can cause some overwood/underwood issues. But if you say you've done the best you can and it's not going to get any better, well, there you go. Either accept that and the end results. Or keep striving for more. Keep in mind, it's your house and your the only one that you have to please.