I say if you can ride a century or back to back weekend 50 mile rides without pain, you are doing well.
I personally want to know my limits so I have experimented with every combination of saddle setback horizontal reach and drop. I have found the pain threshold for me in terms of how aerodynamic I can ride without pain. Every cyclist has a limit for this or everybody would be doing centuries in the TT position on a drop bar bike. Few can however. So generally there is a tradeoff between power, pain and injury. I am mostly limited by neck flexion. Some have more a limited back. Some can ride 5" of drop all day long. So each of us are different and I personally don't think any fitter can put you in an optimal position...only you can find it through exhaustive trial and error.