Andre Turcat reached easy FL680, limit was only his courage. It was on french prototype. Production planes had bit powerfull engines than prototypes. Another his test - reached maximum speed M2.23 (or M2.27 ? I'm not absolutly sure), again, limit was courage.

Original fgaddons Concorde has not speed limit, I made M8 and plane still accelerated. And altitude has hardcap at 103k feets, if I remember correctly. That performance was unacceptable, I changed engine parameters to set limits near Turcat's values. Meassured thrust 10000 lbs at FL510 and M2.04 was unchanged. Empty operational weight (without fuel, pax, crew and cargo) should be 78.7 tons. Official max range was 3700 nm, but in optimal metheo condition Concorde was able fly from SVMI to LFPG - 4100 nm. This was possible only in case of ignore 250 kts restriction under FL100 and climb to FL600 as fast as possible, not with cruise - climb style.

FG probably has not very accurated high altitude atmosphere model, over FL500 is constant -56 degs C. But in reality temperature shoul be bit higher, then Total Ram temperature at aircraft's nose is higher and plane must slow down. Tmo limit vas 128 degs C, what was M2.04 (in FG for Tmo 128 degs C You obtain M2.06).

EDIT :

I checked

http://www.concordesst.com/weight.htmlMax Weight Without Fuel (Zero fuel weight) 203,000 lbs (92,080 kgs)

Operating Weight Empty 173,500 lbs (78,700 kgs)

Max Payload 29,500 lbs (13,380 kgs)

Max Take Off Weight 408,000 lbs (185,000 kgs)

Max taxing Weight 412,000 lbs (186,880 kgs)

Max Landing Weight 245,000 lbs (111,130 kgs)

Max Weight of Fuel 26,400 gallons <=>95,680 kgs

Max baggage weight (under floor hold : forward of door) 2,194 lbs (995 kgs)

Max baggage weight (under floor hold : aft of door) 1,290 lbs (585 kgs)

Max baggage weight (Rear Hold : Lashed) 6,100 lbs (2,767 kgs)

Max baggage weight (Rear Hold : Un-Lashed) 5,000 lbs (2,268 kgs)

In FG, Concorde is configured for maximum pax and maximum cargo, ZFW is around 203000 lb.