I have a 520a.
Here in Germany 100LL is about 8$/gal, so we try to run LOP.
With my very limited experience with my plane I just did 1 longer trip of 3hr 45 min to France. In FL 85 she took 12,5 gal/h for 140kn GS. Therhe must be some improvement.
When she is back from the shop I will go for max speed ROP, Christmas is coming…
Any more information out there?