Look for some posts by a member on rx7club named Howard Coleman. He is one of the resident experts on track-suspension setups. He recommended the 10k front / 8k rear spring rates for a street car that would see moderate track time (which is what I am doing) and I can tell you that it is comfortable on the street but brilliant on the track.
I think the Tein Flex is the newer model of the HA, but I am not certain that they retained the same spring rates. If the Flex is 10k/8k, I would seriously consider them if I were you.