One of the cars I crewed for was an ('88 Rx7) we ran the 710's, both the original and newer lots. We found much higher pressures to be the fastest.
We were at 40-42 HOT.
I'd start around 35 cold, utilizing the same balance split front/rear that you currently use. If you are happy with the balance, increase all pressures 1 psi and see if you are faster or slower. If you are slower go back the other way...if you are slower again then your starting point was probably really close to ideal.
When you are testing like this, there is little value in running numerous laps as fuel loads will change, futher don't put more laps on the tires than you need to find out if it is better/worse.
Whatever direction makes you faster keep going that direction until you start to slow down. Back up a step or two and then see how they behave at those pressures over longer runs.
You may find that while a lower (say 32 HOT) and a higher (say 42 HOT) pressure might arrive at the same lap times. One setting may be more comfortable. Some drivers may want something a little less nervous feeling, while others may want something more responsive.
Too many variables and tradeoffs between ultimate grip, rolling resistance, feedback, alignment and spring rates for me to give you a concrete answer.
35 Cold is a safe starting point...test, test, test.