This is hard to articulate, but I'll try.

I always consider that most all things your car does takes energy to make that thing happen. This energy is supplied in the form of torque from the motor. Anything that takes energy without effectively moving the car forward steals that much energy / power from your ultimate goal of getting to the stripe. Now, A bias tire with softer sidewalls flexes much more at the sidewall (and I believe in the treadpatch) than a radial tire. Flexing the tire takes energy. This energy that is used to flex the tire is energy that dies in the tire, and is not transferred to the track. The stiffer radial tire flexes less, and thus is more effective at transferring all the energy its recieving into rolling force.

The flex is also what makes them hook, so its a double edged sword. But, as said, as long as the radial tire hooks, you're now using more effective energy to push you forward, as less is spent flexing the tire. I think this same principal can be applied to rear suspension (but thats another discussion).

Also, as far as growth. My philosopy here is that growth will only help if you're at the end of your motor's power range, and it needs more gear. If you're still in your effective power range at the top of the track, then you don't want growth, the lower effective gear ratio offered by the non-growing tire will offer acceleration at a faster rate than the higher effective gear.

These are merely my thoughts as a reasonably intelligent person, offered up for discussion. Your thoughts may vary.