Bernie:
Yah, experimentation is the key here. The thing we have to watch is the concavity or convexity of the tread due to low or high PSI pressure. This could cause long life wear problems however, not too many of us seem to care about tire tread life (LOL).
What tire brand are you running and are your shocks/coil overs adjustable in any way? This also is a factor in ride.
I am running 265-50-15 in the front and 305-50-15 in the rear on Halibrand pin drives.
Even though I say the drive quality is "soft" that still has to be couched with the fact that if I drive over a leaf laying on the road I still know it. I mean the ride is firm for sure just not jarring.
If you find a real large parking lot that is vacant (and near some air pump) you may be able to do some informal skid pad work and quickly get dialed in for cornering pressures. That is a good way to find out when the rear breaks and what the car's characteristics are when you take your foot off the gas when cornering fast. (caution with that BTW).
Also, what engine do you have? A big block or small block?
At times, I wish I had a "virtual" Cobra to drive where I can reconfigure it with different brands of tires, rear drive ratio gears, cam, carbs, trannies, shock settings, springs, gas payloads, etc.
Those are a lot of variables which I would LOVE to play around with.
Cheers Bern.