boot flex numbers are a good starting point for discussion. boot flex numbers are like a$$h*%les and some skiers have more than one!
the way a boot flexes for each one of us depends on many more factors than just what the supplier calls the boot. Your height, weight, relative strength that you are capable of driving through the boot, shape of your foot/lower leg, inherent flexibility of your ankle joint, your ability to sense balance and pressure, etc, etc, etc, are all factors that influence your ability to flex a boot.
you will receive feedback on this forum that is all over the map in terms of what each member does or feels about boot flex. that is because each individual skier has their own shape, style, strength, technique, that they push through the boot.
to find yours, start with a well balanced boot that is on the high side of the flex spectrum and start the process of fine tuning by skiing the boot in as many situations and conditions that you can, then begin to tweak the flex/fit in small increments until it works for you in your range of skis, conditions, and temperatures.