My whole point about crz level was on very heavy aircraft crossing temp/wind zones and the sudden narrowing of the overspeed/under speed margin.
Our EFB provides us with a very accurate MAC because we use allocated seating and know where the passengers are seated re zone a,b,& c we subtract 4% from the MAC for FMC perf page and can re calculate inflight after fuel burn off if necessary
This from Boeing FCTM
Maximun Altitude
Maximun altitude at which the aircraft can be operated, It is determined by 3 basic characteristics (for each model) The FMC max altitude is the lowest of
. max certified altitude
.thrust limited altitude - the altitude at which sufficient thrust is available to provide a specific minimum rate of climb (depending on the thrust rating of the engines), the thrust limited altitude may be above or below the manoeuvre capability
. buffet or manoeuvre limited altitude
Although each of these limits are checked by the FMC , available thrust may limit the ability to accomplish anything other than relatively minor manoeuvring. The amber band limits do not provide an indication of manoeuvre capability as limited by thrust.
NOTE to get the most accurate altitude limits from the FMC ensure airplane weight, CRZ CG and temp entries are correct
You provide some interesting and thought provoking comments and i always welcome that from anyone, but you are in my humble opinion acting in a manner that at best will confuse and more likely intimidate your co-pilot, i would be very interested to know if your company procedures allow you to do this and exceeding the FMC derived maximum altitude its is done with blessing of your pilot/training management? the fact that the aircraft may be able to achieve it secondary to the limitations and what do you suppose would happen to you and your co following an high altitude upset where upon the FDM showed that your were above the max altitude? the reason for the upset is not relevant but if there were injuries arising from the recovery then i suspect the lawyers would have a field day, so why Capt Kirk did you think this was a good idea?
Don't get me wrong, i don't doubt that you are a committed and experienced Capt but the fact that your F/o's are having to be re educated by you on the subject of high altitude flights suggests either your training department is at error or dare i suggest it without offending you that perhaps you should reflect upon your own style of operation
Either way fly safe 41'000 is for biz jets or big aeroplanes with big donks
PS the next update of the FMC will provide a thrust limited altitude for manoeuvre