Hi Kitesplosh,
Flex is so complex in a board as the board can flex in so many different ways. The right board for you will be the one that feels best in the conditions you ride in.
The old boards (like yours) are quite stiff and give a hard ride, lots of chattering in the knees and harsh on landings and in nasty chop. They will throw you ok when you stomp the tail but energy is lost as the tail wont flex back and assist you.
The current boards all differ heaps in flex and where and how they flex. A good board should have progressive flex as the board tapers.
Lots of flex smooths out nasty chop by absorbing a lot of the impact and movement of the waves. They feel great for freeriding and carving as the harder you carve the board, the more the board flexes to take the shape of the carve radius. These 'soft' boards are nice to ride so long as you don't want to freestyle. The excessive flex will absorb the energy in the stomp on the tail.
A very stiff board will be uncomfortable to ride but will probably go upwind well and will possibly be fast depending on bottom shape and rails.
The board with 3D flex patterns and contours to allow the tips to flex more and the centre to remain fairly stiff will give you much better loading and reflex (when the board snaps back to it's shape) when you stomp the tail to load and release (I hate the word 'pop'). The centre of the board remains stiff to give good speed and upwind ability.
At the end of the day, grab as many boards as you can to demo and test ride each one in your home conditions, that way you'll know for sure what is your ride.
Hope this helps,