The flex is only part of the equation. For me, I feel the weight of the racquet is more important, as well as the string.
When I started playing with a light racquet (300g) and a stiff string, I immediately started to develop a case of tennis elbow.
Now I play with a 350g racquet with a relatively high flex rating of 68, and everything is just fine.
But you are absolutely right that your technique has a lot to do with it.
Hitting with a heavy racquet, long swing and a relaxed grip, allows the racquet to absorb all the shock of the impact, instead of transmitting it to your arm.
Wilson BLX ProStaff 90: 368g, 7pHL, SW=352. (Wilson NXT 49lb / Lux AluPower 45lb).