I didn't find it in the manuals, but is there an aprox? is it from the real 767 (around 5,505 nm)?
I have found that its range appears to be around 5,800 - 5,900 nm when I use a CI of 0 (zero).

Personally, the longest flight I've done with this 763 is THU (Greenland) to HNL, making 4,146.6 nm in 8h 45m with 132,039.5 pounds of fuel and just enough fuel left to make a go-around.
I have done a flight from MEL to HNL (about 4,870 nm) and landed with about 15,000 to 20,000 pounds of fuel remaining. I started with 160,261 (100%) pounds of fuel and the 763 at almost Maximum Weight (412,000 pounds). The flight took 11.2 hours, I was using a CI of 0.

For example, if I want to make it from SCL (Santiago de Chile) to SYD (around 6,200 nm), is it smart/alright to set your CI at whatever for climb and bring it down up there for an economical cruise at aprox .78 Mach to see how it does? Is this situation just experimental?
I'm not sure if it is allowed in the real world, but I often takeoff with a CI of 0, increase the CI to 40 or 50 for the flight, then reset the CI back to 0 for the descent and landing. A CI of 0 seems to make the 763 climb to cruise altitude faster as well as descend faster. The TC and TD distances are shorter.

How do your long-range flights perform?
Mine perform very nicely. Never had any problems. I use ASE for real weather. I also set my STEP CLIMBS from ICAO to 2000 as this seems to extend the range a bit as well.

Mark