A jet transport lives between two limits: drag and stall at the slow end, compressibility and buffet at the fast end. Fly an A320-sized wing through the drag curve, push the Mach number until shock waves form, find the coffin corner at altitude, and see what the swept wing buys and what it costs.
Total drag is the sum of induced drag, which falls with speed, and parasite drag, which rises with it. The bottom of the curve is the minimum drag speed. For the aerofoil and the stall itself, see the wind tunnel.
The speed of sound depends only on temperature, so it falls as you climb. The airspeed indicator works on dynamic pressure, the wing feels Mach number. A climb at constant IAS therefore ends in a climb at constant Mach.
The machmeter needs no thermometer. It compares the dynamic pressure with the static pressure, and that ratio depends only on the Mach number.
At every altitude there is a low-speed buffet limit (the wing near the stall) and a high-speed buffet limit (shock-induced separation). Climb, add mass or pull g and the two close in until there is no gap left.
Sweep makes the wing see only the part of the airflow that is at right angles to the leading edge. That delays the shock waves, but it also sends air outboard along the span, and that has consequences at low speed and in yaw.
In normal law the A320 protects its angle of attack. After an air data failure, in alternate or direct law, it can stall like any other aircraft, and at high level the recovery is slow and costs thousands of feet. Start a stall at altitude and choose how you recover.
Teaching model of an A320-sized aircraft in the ISA (wing area 122.6 m², drag polar CD = 0.020 + 0.040 CL² clean, wave drag from a simple Lock-type law, a simplified buffet boundary). All numbers are illustrative typical values, not FCOM or AFM data. Real limits come from the FCOM, the AFM and the FMS (MAX and REC MAX altitudes, VLS, green dot).