The answer depends a lot on what specific type and model you are flying. For example some B777s are thrust limited and some are maneuver margin limited . The older B777-200, -200ER, and -300 are thrust limited airplanes and I used to teach not to go more than 2000 above optimum. The newer -300ER, 200F, and 200LR are maneuver margin limited.
Another set of factors is what is set in the airline policy and the CRZ CG in the FMS. The maneuver margin set in the older 777s is often 1.2G, while in the newer models it is set at 1.3G. CRZ CG in the older B777s is set at 30% while Boeing initially set 7.5% in the -300ER. All of these settings have a big impact on what the Maximum altitude will show and on the amber bands of the Airspeed tape. Understanding what they are set at and why is important prior to making absolute statements about how close you will come to the margin.
The B777-300ER is set very conservatively at 1.3G and (was) 7.5% (some operators now set higher numbers). That caused the Maximum altitude to often times show only 1500-1600 feet above optimum. Going back to the older models where Maximum Altitude was often 3500 feet above optimum shows quite a large difference.
Again, the older B777s were thrust limited so going more than 2000 feet above optimum would be risky if you ever got into any situation that caused a speed decay (turbulence, mountain wave, etc). On the newer models the reason given by Boeing for the more conservative settings was "an undesirable vibration" encountered in flight test. This was an airflow related vibration when maneuvering at altitudes greater than about 1500-1600 feet above optimum. Since the newer models are not thrust limited going to within 100-200 feet of Maximum is really a non-issue. It looks kind of scary on the Airspeed display because the amber bands are almost touching, but there really are zero performance related concerns operating that close to Maximum (and again it would only be 1400ish feet above Optimum).
Quite a few of the more senior captains at my old airline would often reset the CRZ CG on the B777-300ER to the old 30% or maybe even the actual CG in order to get a higher altitude sooner, especially when crossing India and the choice was either FL360 or FL280. These guys knew the reason for the conservative setting (there used to be a bulletin explaining it) and they also had a lot of experience operating the older B777s models so knew that going 1800-1900 above Optimum is pretty much a non-issue, especially when it meant getting out of turbulence or to avoid getting a very low cruising level as an alternative. Not saying that I recommend doing that, but it was known occur.
Last edited by typhoonpilot; 26th November 2017 at 08:05.
Reason: Clarification